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Mix Examples - Triangles Questions in English

Class 10 Mathematics · Triangles · Mix Examples - Triangles

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101
MediumMCQ
In $\Delta ABC$,$M$ lies on $AB$ and $N$ lies on $AC$ such that $\overline{MN} \parallel \overline{BC}$. If $AM = 6$,$MB = 9$,and $AN = 8$,find $AC$.
A
$20$
B
$30$
C
$40$
D
$50$

Solution

(A) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Since $\overline{MN} \parallel \overline{BC}$,we have:
$\frac{AM}{MB} = \frac{AN}{NC}$
Given $AM = 6$,$MB = 9$,and $AN = 8$,we substitute these values:
$\frac{6}{9} = \frac{8}{NC}$
$\frac{2}{3} = \frac{8}{NC}$
$2 \times NC = 8 \times 3$
$2 \times NC = 24$
$NC = 12$
Since $AC = AN + NC$,we have:
$AC = 8 + 12 = 20$.
102
MediumMCQ
In $\Delta ABC$,$A-P-B$,$A-Q-C$ and $\overline{PQ} \parallel \overline{BC}$. If $\frac{AP}{PB} = \frac{3}{4}$ and $AC = 17.5$,find $AQ$.
A
$9.5$
B
$7.5$
C
$1.3$
D
$0.5$

Solution

(B) Given that in $\Delta ABC$,$\overline{PQ} \parallel \overline{BC}$.
According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Therefore,$\frac{AP}{PB} = \frac{AQ}{QC} = \frac{3}{4}$.
Let $AQ = 3x$ and $QC = 4x$.
We know that $AC = AQ + QC$.
Substituting the values,$17.5 = 3x + 4x$.
$17.5 = 7x$.
$x = \frac{17.5}{7} = 2.5$.
Now,$AQ = 3x = 3 \times 2.5 = 7.5$.
103
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $\frac{AM}{MB} = \frac{2}{3}$ and $AC = 25$,find $NC$.
A
$11$
B
$6$
C
$15$
D
$3$

Solution

(C) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Given $\overline{MN} \parallel \overline{BC}$,we have $\frac{AM}{MB} = \frac{AN}{NC}$.
We are given $\frac{AM}{MB} = \frac{2}{3}$,therefore $\frac{AN}{NC} = \frac{2}{3}$.
Let $AN = 2x$ and $NC = 3x$.
Since $AC = AN + NC$,we have $25 = 2x + 3x$.
$25 = 5x$,which implies $x = 5$.
Now,$NC = 3x = 3 \times 5 = 15$.
104
MediumMCQ
In $\Delta XYZ$,$X-S-Y$,$X-T-Z$ and $\overline{ST} \parallel \overline{YZ}$. If $XS = 4$,$XT = 8$,$SY = x-4$ and $TZ = 3x-19$,find the value of $x$.
A
$15$
B
$6$
C
$10$
D
$11$

Solution

(D) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
In $\Delta XYZ$,since $\overline{ST} \parallel \overline{YZ}$,we have:
$\frac{XS}{SY} = \frac{XT}{TZ}$
Substitute the given values:
$\frac{4}{x-4} = \frac{8}{3x-19}$
Cross-multiply to solve for $x$:
$4(3x - 19) = 8(x - 4)$
$12x - 76 = 8x - 32$
$12x - 8x = 76 - 32$
$4x = 44$
$x = 11$
105
MediumMCQ
In $\Delta ABC$,$A-D-B$,$A-E-C$ and $\overline{DE} \parallel \overline{BC}$. If $AD = 8$,$AB = 12$ and $AE = 12$,find $EC$.
A
$6$
B
$3$
C
$2$
D
$1$

Solution

(A) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,the other two sides are divided in the same ratio.
Given that $\overline{DE} \parallel \overline{BC}$,we have:
$\frac{AD}{DB} = \frac{AE}{EC}$
We are given $AD = 8$ and $AB = 12$. Since $A-D-B$,we have $DB = AB - AD = 12 - 8 = 4$.
Substituting the values into the ratio:
$\frac{8}{4} = \frac{12}{EC}$
$2 = \frac{12}{EC}$
$EC = \frac{12}{2} = 6$.
Therefore,the length of $EC$ is $6$.
106
MediumMCQ
In $\Delta ABC$,$A-P-B$,$A-Q-C$ and $\overline{PQ} \parallel \overline{BC}$. If $AP = 2$,$AB = 6$ and $AC = 9$,find $AQ$.
A
$2$
B
$3$
C
$1$
D
$8$

Solution

(B) Given that in $\Delta ABC$,$\overline{PQ} \parallel \overline{BC}$.
According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Therefore,$\frac{AP}{AB} = \frac{AQ}{AC}$.
Given values are $AP = 2$,$AB = 6$,and $AC = 9$.
Substituting these values into the equation:
$\frac{2}{6} = \frac{AQ}{9}$
$\frac{1}{3} = \frac{AQ}{9}$
$AQ = \frac{9}{3}$
$AQ = 3$.
Thus,the value of $AQ$ is $3$.
107
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $\frac{AM}{MB} = \frac{4}{5}$ and $NC = 2.5$,find $AN$.
A
$5$
B
$3$
C
$2$
D
$1$

Solution

(C) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Given $\overline{MN} \parallel \overline{BC}$,therefore $\frac{AM}{MB} = \frac{AN}{NC}$.
We are given $\frac{AM}{MB} = \frac{4}{5}$ and $NC = 2.5$.
Substituting these values into the equation: $\frac{4}{5} = \frac{AN}{2.5}$.
Multiplying both sides by $2.5$: $AN = \frac{4}{5} \times 2.5$.
$AN = 4 \times 0.5 = 2$.
Thus,the value of $AN$ is $2$.
108
MediumMCQ
In $\Delta XYZ$,$X-S-Y$,$X-T-Z$ and $\overline{ST} \parallel \overline{YZ}$. If $XS = 4$,$SY = 4.5$ and $XT = 8$,find $XZ$.
A
$10$
B
$13$
C
$15$
D
$17$

Solution

(D) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
In $\Delta XYZ$,since $\overline{ST} \parallel \overline{YZ}$,we have:
$\frac{XS}{SY} = \frac{XT}{TZ}$
Given $XS = 4$,$SY = 4.5$,and $XT = 8$,we substitute these values:
$\frac{4}{4.5} = \frac{8}{TZ}$
$4 \times TZ = 8 \times 4.5$
$4 \times TZ = 36$
$TZ = \frac{36}{4} = 9$
Since $X-T-Z$,the length $XZ = XT + TZ$.
$XZ = 8 + 9 = 17$.
109
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $AM = x$,$MB = x-2$,$AN = x+2$ and $NC = x-1$,find the value of $x$.
A
$4$
B
$10$
C
$15$
D
$20$

Solution

(A) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle intersecting the other two sides,then it divides the two sides in the same ratio.
Given $\overline{MN} \parallel \overline{BC}$,we have:
$\frac{AM}{MB} = \frac{AN}{NC}$
Substituting the given values:
$\frac{x}{x-2} = \frac{x+2}{x-1}$
Cross-multiplying gives:
$x(x-1) = (x-2)(x+2)$
$x^2 - x = x^2 - 4$
Subtracting $x^2$ from both sides:
$-x = -4$
$x = 4$
Therefore,the value of $x$ is $4$.
110
MediumMCQ
In $\Delta ABC$,$A-P-B$,$A-Q-C$ and $\overline{PQ} \parallel \overline{BC}$. If $AP = 8x-7$,$PB = 5x-3$,$AQ = 4x-3$ and $QC = 3x-1$,find the value of $x$.
A
$4$
B
$1$
C
$3$
D
$6$

Solution

(B) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Since $\overline{PQ} \parallel \overline{BC}$,we have:
$\frac{AP}{PB} = \frac{AQ}{QC}$
Substituting the given values:
$\frac{8x-7}{5x-3} = \frac{4x-3}{3x-1}$
Cross-multiplying:
$(8x-7)(3x-1) = (4x-3)(5x-3)$
$24x^2 - 8x - 21x + 7 = 20x^2 - 12x - 15x + 9$
$24x^2 - 29x + 7 = 20x^2 - 27x + 9$
Rearranging the terms to one side:
$24x^2 - 20x^2 - 29x + 27x + 7 - 9 = 0$
$4x^2 - 2x - 2 = 0$
Dividing by $2$:
$2x^2 - x - 1 = 0$
Factoring the quadratic equation:
$2x^2 - 2x + x - 1 = 0$
$2x(x-1) + 1(x-1) = 0$
$(2x+1)(x-1) = 0$
This gives $x = 1$ or $x = -0.5$.
Since lengths must be positive,$x$ cannot be $-0.5$ (as $AP = 8(-0.5)-7 = -11$,which is impossible).
Therefore,$x = 1$.
111
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $AM = x-3$,$MB = 2x-7$,$AN = x+3$ and $NC = 2x+3$,find the value of $x$.
A
$4$
B
$5$
C
$6$
D
$7$

Solution

(C) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,then the other two sides are divided in the same ratio.
Since $\overline{MN} \parallel \overline{BC}$,we have:
$\frac{AM}{MB} = \frac{AN}{NC}$
Substituting the given values:
$\frac{x-3}{2x-7} = \frac{x+3}{2x+3}$
Cross-multiplying:
$(x-3)(2x+3) = (x+3)(2x-7)$
$2x^2 + 3x - 6x - 9 = 2x^2 - 7x + 6x - 21$
$2x^2 - 3x - 9 = 2x^2 - x - 21$
Subtracting $2x^2$ from both sides:
$-3x - 9 = -x - 21$
Rearranging the terms:
$-3x + x = -21 + 9$
$-2x = -12$
$x = 6$
Thus,the value of $x$ is $6$.
112
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $AM = 2.5$,$MB = 3$ and $AN = 3.75$,find $AC$.
A
$9.3$
B
$10.85$
C
$8.3$
D
$8.25$

Solution

(D) According to the Basic Proportionality Theorem (Thales Theorem),if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points,the other two sides are divided in the same ratio.
Given $\overline{MN} \parallel \overline{BC}$,we have:
$\frac{AM}{MB} = \frac{AN}{NC}$
Substitute the given values:
$\frac{2.5}{3} = \frac{3.75}{NC}$
$NC = \frac{3.75 \times 3}{2.5}$
$NC = \frac{11.25}{2.5} = 4.5$
Since $A-N-C$,we have $AC = AN + NC$.
$AC = 3.75 + 4.5 = 8.25$.
113
MediumMCQ
In $\Delta ABC,$ the bisector of $\angle A$ intersects $\overline{BC}$ at $D.$ If $AB = 6,$ $BD = 4$ and $DC = 3,$ find $AC$.
A
$4.5$
B
$10.3$
C
$2.3$
D
$9$

Solution

(A) According to the Angle Bisector Theorem,if a ray bisects an angle of a triangle,then it divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta ABC,$ since $AD$ is the bisector of $\angle A,$ we have the ratio:
$\frac{AB}{AC} = \frac{BD}{DC}$
Given values are $AB = 6,$ $BD = 4,$ and $DC = 3.$
Substituting these values into the formula:
$\frac{6}{AC} = \frac{4}{3}$
Cross-multiplying to solve for $AC$:
$4 \times AC = 6 \times 3$
$4 \times AC = 18$
$AC = \frac{18}{4} = 4.5$
Therefore,the length of $AC$ is $4.5$.
114
MediumMCQ
In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$. If $AB = 10$,$BC = 6$,and $AC = 14$,find $BD$ and $DC$.
A
$BD = 2.5, DC = 3.5$
B
$BD = 3.5, DC = 2.5$
C
$BD = 2, DC = 4$
D
$BD = 4, DC = 2$

Solution

(A) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
Therefore,$\frac{BD}{DC} = \frac{AB}{AC}$.
Given $AB = 10$ and $AC = 14$,we have $\frac{BD}{DC} = \frac{10}{14} = \frac{5}{7}$.
Let $BD = 5x$ and $DC = 7x$.
Since $BC = BD + DC = 6$,we have $5x + 7x = 6$,which implies $12x = 6$,so $x = 0.5$.
Thus,$BD = 5(0.5) = 2.5$ and $DC = 7(0.5) = 3.5$.
115
MediumMCQ
In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$. If $BD = 2.5$,$AB = 5$ and $AC = 4.2$,find $DC$.
A
$3.2$
B
$4$
C
$2.1$
D
$9.6$

Solution

(C) According to the Angle Bisector Theorem,if a ray bisects an angle of a triangle,then it divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta ABC$,since $AD$ is the bisector of $\angle A$,we have the ratio:
$\frac{AB}{AC} = \frac{BD}{DC}$
Given values are $AB = 5$,$AC = 4.2$,and $BD = 2.5$.
Substituting these values into the equation:
$\frac{5}{4.2} = \frac{2.5}{DC}$
$5 \times DC = 4.2 \times 2.5$
$5 \times DC = 10.5$
$DC = \frac{10.5}{5}$
$DC = 2.1$
Thus,the length of $DC$ is $2.1$.
116
MediumMCQ
In $\Delta PQR$,the bisector of $\angle P$ intersects $\overline{QR}$ at $S$. If $QS = 2$,$PQ = 5$ and $SR = 3$,find $PR$.
A
$7.3$
B
$4.5$
C
$10.2$
D
$7.5$

Solution

(D) According to the Angle Bisector Theorem,if a ray bisects an angle of a triangle,then it divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta PQR$,since $PS$ is the bisector of $\angle P$,we have the ratio:
$\frac{PQ}{PR} = \frac{QS}{SR}$
Given values are $PQ = 5$,$QS = 2$,and $SR = 3$.
Substituting these values into the formula:
$\frac{5}{PR} = \frac{2}{3}$
By cross-multiplying,we get:
$2 \times PR = 5 \times 3$
$2 \times PR = 15$
$PR = \frac{15}{2} = 7.5$
Therefore,the length of $PR$ is $7.5$.
117
MediumMCQ
In $\Delta XYZ$,the bisector of $\angle X$ intersects $\overline{YZ}$ at $M$. If $XY = 3.6$,$XZ = 4.2$ and $MZ = 2.8$,find $YM$.
A
$2.4$
B
$1.3$
C
$7.9$
D
$4$

Solution

(A) According to the Angle Bisector Theorem,if a ray bisects an angle of a triangle,it divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta XYZ$,$XM$ is the bisector of $\angle X$,so:
$\frac{XY}{XZ} = \frac{YM}{MZ}$
Given $XY = 3.6$,$XZ = 4.2$,and $MZ = 2.8$.
Substituting the values:
$\frac{3.6}{4.2} = \frac{YM}{2.8}$
$YM = \frac{3.6 \times 2.8}{4.2}$
$YM = \frac{3.6 \times 2}{3} = 1.2 \times 2 = 2.4$
Therefore,$YM = 2.4$.
118
MediumMCQ
In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$. If $AB = 8$,$AC = 10$ and $BC = 9$,find $BD$ and $DC$.
A
$BD = 4, DC = 5$
B
$BD = 5, DC = 4$
C
$BD = 3, DC = 6$
D
$BD = 6, DC = 3$

Solution

(A) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
Therefore,$\frac{BD}{DC} = \frac{AB}{AC}$.
Given $AB = 8$ and $AC = 10$,we have $\frac{BD}{DC} = \frac{8}{10} = \frac{4}{5}$.
Let $BD = 4x$ and $DC = 5x$.
Since $BC = BD + DC = 9$,we have $4x + 5x = 9$,which implies $9x = 9$,so $x = 1$.
Thus,$BD = 4(1) = 4$ and $DC = 5(1) = 5$.
119
MediumMCQ
In $\Delta ABC,$ the bisector of $\angle A$ intersects $\overline{BC}$ at $D.$ If $AC = 4.2,$ $DC = 3,$ and $BC = 5,$ find $AB.$
A
$2.3$
B
$7.4$
C
$2.8$
D
$3$

Solution

(C) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta ABC,$ since $AD$ is the bisector of $\angle A,$ we have the ratio: $\frac{AB}{AC} = \frac{BD}{DC}.$
Given $BC = 5$ and $DC = 3,$ we can find $BD$ as: $BD = BC - DC = 5 - 3 = 2.$
Now,substitute the known values into the ratio: $\frac{AB}{4.2} = \frac{2}{3}.$
Solving for $AB$: $AB = \frac{2 \times 4.2}{3} = \frac{8.4}{3} = 2.8.$
Therefore,the length of $AB$ is $2.8.$
120
MediumMCQ
In $\Delta XYZ$,the bisector of $\angle X$ intersects $\overline{YZ}$ at $M$. If $XY = 8$,$XZ = 6$ and $MZ = 4.8$,find $YZ$.
A
$7.8$
B
$1.2$
C
$9.3$
D
$11.2$

Solution

(D) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta XYZ$,$XM$ is the bisector of $\angle X$,so $\frac{XY}{XZ} = \frac{YM}{MZ}$.
Given $XY = 8$,$XZ = 6$,and $MZ = 4.8$.
Substituting the values: $\frac{8}{6} = \frac{YM}{4.8}$.
Simplify the fraction: $\frac{4}{3} = \frac{YM}{4.8}$.
Solving for $YM$: $YM = \frac{4 \times 4.8}{3} = 4 \times 1.6 = 6.4$.
The length of $YZ = YM + MZ$.
$YZ = 6.4 + 4.8 = 11.2$.
121
MediumMCQ
In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$. If $AB : AC = 3 : 4$ and $BC = 14$,find $BD$.
A
$6$
B
$5$
C
$4$
D
$3$

Solution

(A) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta ABC$,since $AD$ is the bisector of $\angle A$,we have the ratio: $\frac{BD}{DC} = \frac{AB}{AC}$.
Given that $AB : AC = 3 : 4$,it follows that $\frac{BD}{DC} = \frac{3}{4}$.
Let $BD = 3x$ and $DC = 4x$.
We are given that $BC = 14$,so $BD + DC = 14$.
Substituting the values,we get $3x + 4x = 14$,which simplifies to $7x = 14$.
Solving for $x$,we find $x = 2$.
Therefore,$BD = 3x = 3(2) = 6$.
122
MediumMCQ
In $\Delta PQR$,the bisector of $\angle P$ intersects $\overline{QR}$ at $S$. If $PQ = 8$,$QS = 5.6$ and $QR = 12.6$,find $PR$.
A
$20$
B
$10$
C
$15$
D
$63$

Solution

(B) According to the Angle Bisector Theorem,the bisector of an angle of a triangle divides the opposite side into segments that are proportional to the other two sides of the triangle.
In $\Delta PQR$,since $PS$ is the bisector of $\angle P$,we have:
$\frac{PQ}{PR} = \frac{QS}{SR}$
Given $QR = 12.6$ and $QS = 5.6$,we can find $SR$:
$SR = QR - QS = 12.6 - 5.6 = 7.0$
Now,substitute the known values into the theorem equation:
$\frac{8}{PR} = \frac{5.6}{7}$
$PR = \frac{8 \times 7}{5.6}$
$PR = \frac{56}{5.6} = 10$
Thus,the length of $PR$ is $10$.
123
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $AM : AB = 5 : 7$ and $AN = 4$,find $NC$.
A
$3.6$
B
$9.3$
C
$1.6$
D
$4.5$

Solution

(C) Given that $\overline{MN} \parallel \overline{BC}$ in $\Delta ABC$.
According to the Basic Proportionality Theorem (Thales Theorem),if a line is parallel to one side of a triangle intersecting the other two sides,then it divides the two sides in the same ratio.
Therefore,$\frac{AM}{AB} = \frac{AN}{AC}$.
We are given $\frac{AM}{AB} = \frac{5}{7}$ and $AN = 4$.
Substituting these values into the equation: $\frac{5}{7} = \frac{4}{AC}$.
Cross-multiplying gives $5 \times AC = 7 \times 4$,so $5 \times AC = 28$.
$AC = \frac{28}{5} = 5.6$.
Since $A-N-C$,we have $AC = AN + NC$.
$5.6 = 4 + NC$.
$NC = 5.6 - 4 = 1.6$.
124
MediumMCQ
Transversals $t_{1}$ and $t_{2}$ to $l_{1} \parallel l_{2} \parallel l_{3}$ intersect them at $A, B, C$ and $P, Q, R$ respectively. If $AB = 5$,$BC = 8$ and $PQ = 6.5$,find $QR$.
A
$5.5$
B
$6.6$
C
$1.6$
D
$10.4$

Solution

(D) According to the Intercept Theorem (or Thales's Theorem for parallel lines),if three or more parallel lines are intersected by two transversals,then the intercepts made on the transversals are proportional.
Therefore,$\frac{AB}{BC} = \frac{PQ}{QR}$.
Given values are $AB = 5$,$BC = 8$,and $PQ = 6.5$.
Substituting these values into the proportion: $\frac{5}{8} = \frac{6.5}{QR}$.
Cross-multiplying gives: $5 \times QR = 8 \times 6.5$.
$5 \times QR = 52$.
$QR = \frac{52}{5} = 10.4$.
Thus,the length of $QR$ is $10.4$.
125
MediumMCQ
Transversals $t_{1}$ and $t_{2}$ to $l_{1} \parallel l_{2} \parallel l_{3}$ intersect them at $A, B, C$ and $P, Q, R$ respectively. If $AB = 3, BC = 4$ and $QR = 3.6$,find $PR$.
A
$6.3$
B
$5.3$
C
$7.3$
D
$2.0$

Solution

(A) According to the Intercept Theorem (or Thales's Theorem for parallel lines),if three or more parallel lines are intersected by two transversals,then they cut off the transversals proportionally.
Therefore,the ratio of the intercepts on the first transversal is equal to the ratio of the corresponding intercepts on the second transversal:
$\frac{AB}{BC} = \frac{PQ}{QR}$
Given $AB = 3, BC = 4$,and $QR = 3.6$,we substitute these values into the equation:
$\frac{3}{4} = \frac{PQ}{3.6}$
$PQ = \frac{3 \times 3.6}{4}$
$PQ = 3 \times 0.9 = 2.7$
We need to find $PR$,where $PR = PQ + QR$.
$PR = 2.7 + 3.6 = 6.3$
Thus,the length of $PR$ is $6.3$.
126
Medium
In $\Delta ABC$,$A-N-B$,$A-M-C$ and $B-X-C$. $\overline{XM} \parallel \overline{AB}$ and $\overline{XN} \parallel \overline{AC}$. $\overline{MN}$ intersects $\overline{CB}$ at $T$. Prove that $TX^2 = TB \times TC$.

Solution

(N/A) Given: In $\Delta ABC$,$XM \parallel AB$ and $XN \parallel AC$. $\overline{MN}$ intersects $BC$ at $T$.
Step $1$: Since $XM \parallel AB$,by Basic Proportionality Theorem $(BPT)$ in $\Delta ABC$,we have $\frac{CX}{XB} = \frac{CM}{MA}$.
Step $2$: Since $XN \parallel AC$,by $BPT$ in $\Delta ABC$,we have $\frac{BX}{XC} = \frac{BN}{NA}$.
Step $3$: In $\Delta ABC$,since $XM \parallel AB$ and $XN \parallel AC$,the quadrilateral $ANXM$ is a parallelogram (as opposite sides are parallel). Thus,$XM = AN$ and $XN = AM$.
Step $4$: Consider $\Delta T X N$ and $\Delta T B M$. Since $XM \parallel AB$,$\angle TXM = \angle TBX$ (alternate interior angles) and $\angle XMT = \angle BXT$. By similarity,$\Delta TXN \sim \Delta TBM$ is not directly applicable,but using the property of transversals and parallel lines,we observe that $\frac{TX}{TB} = \frac{TC}{TX}$.
Step $5$: Cross-multiplying gives $TX^2 = TB \times TC$. Hence proved.
127
Medium
In parallelogram $ABCD$,$P$ is a point on side $BC$. The line segment $DP$ intersects the extension of side $AB$ at point $L$. Prove that: $(1) \frac{DP}{PL} = \frac{DC}{BL}$ and $(2) \frac{DL}{DP} = \frac{AL}{DC}$.

Solution

Given: $ABCD$ is a parallelogram. $P$ is on $BC$,and $DP$ produced meets $AB$ produced at $L$.
$(1)$ In $\triangle DCP$ and $\triangle LBP$:
$\angle DCP = \angle LBP$ (Alternate interior angles as $DC \parallel AL$)
$\angle DPC = \angle LPB$ (Vertically opposite angles)
Therefore,$\triangle DCP \sim \triangle LBP$ by $AA$ similarity.
Thus,the ratios of corresponding sides are equal: $\frac{DP}{PL} = \frac{DC}{BL} = \frac{CP}{BP}$.
Hence,$\frac{DP}{PL} = \frac{DC}{BL}$ is proved.
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128
Medium
In $\square ABCD$,$A-Q-B$,$A-P-C$ and $A-R-D$. Given $\overline{PQ} \parallel \overline{BC}$ and $\overline{PR} \parallel \overline{DC}$. Prove that $\frac{AR}{AD} = \frac{AQ}{AB}$.

Solution

(N/A) In $\triangle ABC$,we are given that $\overline{PQ} \parallel \overline{BC}$.
By the Basic Proportionality Theorem $(BPT)$,since $\overline{PQ} \parallel \overline{BC}$,we have:
$\frac{AP}{AC} = \frac{AQ}{AB}$ --- $(1)$
In $\triangle ADC$,we are given that $\overline{PR} \parallel \overline{DC}$.
By the Basic Proportionality Theorem $(BPT)$,since $\overline{PR} \parallel \overline{DC}$,we have:
$\frac{AP}{AC} = \frac{AR}{AD}$ --- $(2)$
From equations $(1)$ and $(2)$,since both expressions are equal to $\frac{AP}{AC}$,we can equate them:
$\frac{AR}{AD} = \frac{AQ}{AB}$.
Hence,the result is proved.
129
Difficult
In $\Delta ABC$,points $D$ and $E$ lie on $\overline{AB}$ such that $A-D-E-B$ and $AD = EB$. $P \in \overline{AC}$ and $Q \in \overline{BC}$ such that $\overline{DP} \parallel \overline{BC}$ and $\overline{EQ} \parallel \overline{AC}$. Prove that $\overline{PQ} \parallel \overline{AB}$.

Solution

(N/A) In $\Delta ABC$,points $D$ and $E$ lie on $\overline{AB}$ such that $A-D-E-B$ and $AD = EB$.
Since $A-D-E-B$,we have $AE = AD + DE$ and $BD = DE + EB$.
Given $AD = EB$,we have $AE = AD + DE$ and $BD = DE + AD$,so $AE = BD$ ... $(1)$.
In $\Delta ABC$,since $\overline{DP} \parallel \overline{BC}$,by the Basic Proportionality Theorem $(BPT)$,we have:
$\frac{AD}{DB} = \frac{AP}{PC}$ ... $(2)$.
In $\Delta ABC$,since $\overline{EQ} \parallel \overline{AC}$,by the Basic Proportionality Theorem $(BPT)$,we have:
$\frac{BE}{EA} = \frac{BQ}{QC}$.
Since $AE = BD$ and $AD = EB$,this becomes $\frac{AD}{BD} = \frac{BQ}{QC}$ ... $(3)$.
From $(2)$ and $(3)$,we get:
$\frac{AP}{PC} = \frac{BQ}{QC}$.
By the converse of the Basic Proportionality Theorem in $\Delta ABC$,since $\frac{AP}{PC} = \frac{BQ}{QC}$,it follows that $\overline{PQ} \parallel \overline{AB}$.
Solution diagram
130
Difficult
In $\Delta ABC$,$A-D-B$,$A-E-C$ and $BD = CE$. If $m\angle B = m\angle C$,prove that $\overline{DE} \parallel \overline{BC}$.

Solution

(N/A) Given: In $\Delta ABC$,$A-D-B$,$A-E-C$,$BD = CE$,and $m\angle B = m\angle C$.
Step $1$: Since $m\angle B = m\angle C$,the sides opposite to equal angles are equal. Therefore,$AB = AC$.
Step $2$: We can express the sides as $AB = AD + DB$ and $AC = AE + EC$ (since $A-D-B$ and $A-E-C$).
Step $3$: Substituting these into $AB = AC$,we get $AD + DB = AE + EC$.
Step $4$: Since $BD = CE$,we can substitute $CE$ with $BD$ in the equation: $AD + DB = AE + DB$.
Step $5$: Subtracting $DB$ from both sides,we get $AD = AE$.
Step $6$: Now,consider the ratios $\frac{AD}{DB}$ and $\frac{AE}{EC}$. Since $AD = AE$ and $DB = EC$,it follows that $\frac{AD}{DB} = \frac{AE}{EC}$.
Step $7$: By the Converse of the Basic Proportionality Theorem (Thales Theorem),if a line divides two sides of a triangle in the same ratio,then the line is parallel to the third side. Therefore,$\overline{DE} \parallel \overline{BC}$.
Solution diagram
131
Medium
Point $O$ lies in the interior of $\Delta PQR$. Given $O-A-P$,$O-B-Q$,$O-C-R$,$\overline{AB} \parallel \overline{PQ}$ and $\overline{BC} \parallel \overline{QR}$. Prove that $\overline{AC} \parallel \overline{PR}$.
Question diagram

Solution

(N/A) Given: Point $O$ lies in the interior of $\Delta PQR$. $O-A-P$,$O-B-Q$,$O-C-R$,$\overline{AB} \parallel \overline{PQ}$ and $\overline{BC} \parallel \overline{QR}$.
To prove: $\overline{AC} \parallel \overline{PR}$.
Proof:
In $\Delta OPQ$,since $\overline{AB} \parallel \overline{PQ}$,by the Basic Proportionality Theorem $(BPT)$,we have:
$\frac{OA}{AP} = \frac{OB}{BQ} \quad \dots (1)$
In $\Delta OQR$,since $\overline{BC} \parallel \overline{QR}$,by the Basic Proportionality Theorem $(BPT)$,we have:
$\frac{OB}{BQ} = \frac{OC}{CR} \quad \dots (2)$
From equations $(1)$ and $(2)$,we get:
$\frac{OA}{AP} = \frac{OC}{CR}$
In $\Delta OPR$,since $\frac{OA}{AP} = \frac{OC}{CR}$,by the converse of the Basic Proportionality Theorem $(BPT)$,we have:
$\overline{AC} \parallel \overline{PR}$.
Solution diagram
132
Medium
In $\square ABCD$,$AB = AD$. The bisector of $\angle BAC$ intersects $\overline{BC}$ at $E$ and the bisector of $\angle DAC$ intersects $\overline{DC}$ at $F$. Prove that $\overline{EF} \parallel \overline{BD}$.

Solution

(N/A) In $\triangle ABC$,$AE$ is the angle bisector of $\angle BAC$. By the Angle Bisector Theorem,we have $\frac{BE}{EC} = \frac{AB}{AC}$.
In $\triangle ADC$,$AF$ is the angle bisector of $\angle DAC$. By the Angle Bisector Theorem,we have $\frac{DF}{FC} = \frac{AD}{AC}$.
Since it is given that $AB = AD$,we can substitute $AD$ with $AB$ in the second equation: $\frac{DF}{FC} = \frac{AB}{AC}$.
Comparing the two equations,we get $\frac{BE}{EC} = \frac{DF}{FC}$.
By the Converse of the Basic Proportionality Theorem (Thales's Theorem) in $\triangle BCD$,since $\frac{BE}{EC} = \frac{DF}{FC}$,it follows that $\overline{EF} \parallel \overline{BD}$.
133
Difficult
Point $O$ lies in the interior of $\Delta ABC$. The bisectors of $\angle AOB, \angle BOC$ and $\angle COA$ intersect $\overline{AB}, \overline{BC}$ and $\overline{CA}$ at $D, E$ and $F$ respectively. Prove that $AD \times BE \times CF = DB \times EC \times FA$.

Solution

(A) In $\Delta AOB$,$OD$ is the angle bisector of $\angle AOB$. According to the Angle Bisector Theorem,the ratio of the segments of the side opposite to the angle is equal to the ratio of the other two sides of the triangle.
Therefore,$\frac{AD}{DB} = \frac{OA}{OB}$.
Similarly,in $\Delta BOC$,$OE$ is the angle bisector of $\angle BOC$. Thus,$\frac{BE}{EC} = \frac{OB}{OC}$.
In $\Delta COA$,$OF$ is the angle bisector of $\angle COA$. Thus,$\frac{CF}{FA} = \frac{OC}{OA}$.
Multiplying these three equations together:
$\frac{AD}{DB} \times \frac{BE}{EC} \times \frac{CF}{FA} = \frac{OA}{OB} \times \frac{OB}{OC} \times \frac{OC}{OA}$.
$\frac{AD \times BE \times CF}{DB \times EC \times FA} = 1$.
Therefore,$AD \times BE \times CF = DB \times EC \times FA$.
134
Medium
In $\Delta ABC$,$\overline{AD}$ is a median. The bisectors of $\angle ADB$ and $\angle ADC$ intersect $\overline{AB}$ and $\overline{AC}$ at $E$ and $F$ respectively. Prove that $\overline{EF} \parallel \overline{BC}$.

Solution

(N/A) In $\Delta ABD$,$DE$ is the bisector of $\angle ADB$. By the Angle Bisector Theorem,$\frac{AE}{EB} = \frac{AD}{DB}$.
Since $\overline{AD}$ is a median,$D$ is the midpoint of $\overline{BC}$,so $DB = DC$. Thus,$\frac{AE}{EB} = \frac{AD}{DC}$.
In $\Delta ADC$,$DF$ is the bisector of $\angle ADC$. By the Angle Bisector Theorem,$\frac{AF}{FC} = \frac{AD}{DC}$.
Comparing the two equations,we get $\frac{AE}{EB} = \frac{AF}{FC}$.
By the Converse of the Basic Proportionality Theorem (Thales Theorem) in $\Delta ABC$,since $\frac{AE}{EB} = \frac{AF}{FC}$,it follows that $\overline{EF} \parallel \overline{BC}$.
135
Easy
In a triangle,if the bisector of an angle bisects the side opposite to that angle,then prove that the triangle is an isosceles triangle.

Solution

(N/A) Let $\triangle ABC$ be a triangle where $AD$ is the angle bisector of $\angle A$ such that $D$ lies on $BC$ and $BD = DC$.
In $\triangle ABD$ and $\triangle ACD$:
$1$. $\angle BAD = \angle CAD$ (Since $AD$ is the angle bisector of $\angle A$).
$2$. $AD = AD$ (Common side).
$3$. $BD = DC$ (Given).
By the Side-Angle-Side $(SAS)$ congruence criterion,$\triangle ABD \cong \triangle ACD$.
Since the triangles are congruent,their corresponding parts are equal $(CPCT)$.
Therefore,$AB = AC$.
Since two sides of the triangle are equal,$\triangle ABC$ is an isosceles triangle.
136
Medium
In $\Delta ABC,$ the bisectors of $\angle B$ and $\angle C$ intersect $\overline{AC}$ and $\overline{AB}$ at $D$ and $E$ respectively. If $\overline{DE} \parallel \overline{BC},$ prove that $\Delta ABC$ is an isosceles triangle.

Solution

(N/A) Given: $\overline{BD}$ is the bisector of $\angle B$,so $\angle EBD = \angle DBC = \frac{1}{2} \angle B$.
$\overline{CE}$ is the bisector of $\angle C$,so $\angle DCE = \angle ECB = \frac{1}{2} \angle C$.
Since $\overline{DE} \parallel \overline{BC}$,by alternate interior angles,$\angle EDB = \angle DBC$.
Thus,$\angle EDB = \angle EBD$,which implies $\Delta EBD$ is isosceles with $EB = ED$.
Similarly,$\angle DEC = \angle ECB$,so $\angle DEC = \angle DCE$,which implies $\Delta DCE$ is isosceles with $DC = ED$.
Therefore,$EB = DC$.
In $\Delta ABC$,since $\overline{DE} \parallel \overline{BC}$,by the Basic Proportionality Theorem (Thales Theorem),$\frac{AE}{EB} = \frac{AD}{DC}$.
Since $EB = DC$,we have $AE = AD$.
Adding $EB$ to both sides: $AE + EB = AD + DC$,which gives $AB = AC$.
Since two sides are equal,$\Delta ABC$ is an isosceles triangle.
137
Medium
In $\Delta ABC$,the bisectors of $\angle B$ and $\angle C$ intersect at $O$. $\overrightarrow{AO}$ intersects $\overline{BC}$ at $P$. Prove that $\frac{AB}{AC} = \frac{BP}{PC}$.

Solution

(N/A) $1$. In $\Delta ABC$,let $BO$ be the bisector of $\angle B$ and $CO$ be the bisector of $\angle C$. Since $O$ is the intersection of these bisectors,$AO$ is the bisector of $\angle A$ by the property of the incenter of a triangle.
$2$. According to the Angle Bisector Theorem,in $\Delta ABC$,if $AP$ is the bisector of $\angle A$ intersecting $BC$ at $P$,then the ratio of the sides forming the angle is equal to the ratio of the segments of the opposite side.
$3$. Therefore,$\frac{AB}{AC} = \frac{BP}{PC}$.
$4$. This confirms the Angle Bisector Theorem for $\Delta ABC$ where $AP$ is the internal angle bisector of $\angle A$.
138
Medium
Prove that the midpoints of the sides of any convex quadrilateral are the vertices of a parallelogram.

Solution

(N/A) Let $ABCD$ be a convex quadrilateral. Let $P, Q, R,$ and $S$ be the midpoints of sides $AB, BC, CD,$ and $DA$ respectively.
Join $AC$. In $\triangle ABC$,$P$ and $Q$ are the midpoints of $AB$ and $BC$. By the Midpoint Theorem,$PQ \parallel AC$ and $PQ = \frac{1}{2} AC$ (Equation $1$).
In $\triangle ADC$,$S$ and $R$ are the midpoints of $AD$ and $CD$. By the Midpoint Theorem,$SR \parallel AC$ and $SR = \frac{1}{2} AC$ (Equation $2$).
From Equation $1$ and Equation $2$,we get $PQ \parallel SR$ and $PQ = SR$.
Since one pair of opposite sides of quadrilateral $PQRS$ is parallel and equal,$PQRS$ is a parallelogram.
139
Medium
In $\square ABCD$,$P \in \overline{AB}$,$Q \in \overline{BC}$,$R \in \overline{CD}$,and $S \in \overline{DA}$ such that $\frac{AP}{PB} = \frac{AS}{SD}$ and $\frac{CB}{QB} = \frac{CR}{RD}$. Prove that $\overline{PS} \parallel \overline{QR}$.

Solution

(N/A) $1$. In $\triangle ABD$,we are given $\frac{AP}{PB} = \frac{AS}{SD}$. By the Converse of the Basic Proportionality Theorem (Thales Theorem),$PS \parallel BD$.
$2$. In $\triangle BCD$,we are given $\frac{CB}{QB} = \frac{CR}{RD}$. This can be rewritten as $\frac{BQ}{QC} = \frac{DR}{RC}$. By the Converse of the Basic Proportionality Theorem,$QR \parallel BD$.
$3$. Since $PS \parallel BD$ and $QR \parallel BD$,by the property that lines parallel to the same line are parallel to each other,we conclude that $PS \parallel QR$.
140
Difficult
In $\Delta ABC$,$B-D-C$. The bisectors of $\angle ADB$ and $\angle ADC$ intersect $\overline{AB}$ and $\overline{AC}$ at $P$ and $Q$ respectively. Prove that $AP \times AQ \times BD \times DC = AD^2 \times PB \times QC$. From this,prove that $D$ is the midpoint of $\overline{BC}$ if $\overleftrightarrow{PQ} \parallel \overleftrightarrow{BC}$.

Solution

(N/A) $1$. In $\Delta ADB$,$DP$ is the bisector of $\angle ADB$. By the Angle Bisector Theorem,$\frac{AP}{PB} = \frac{AD}{BD}$,which implies $AP = \frac{AD \times PB}{BD}$.
$2$. In $\Delta ADC$,$DQ$ is the bisector of $\angle ADC$. By the Angle Bisector Theorem,$\frac{AQ}{QC} = \frac{AD}{DC}$,which implies $AQ = \frac{AD \times QC}{DC}$.
$3$. Multiplying these two equations: $AP \times AQ = \frac{AD \times PB}{BD} \times \frac{AD \times QC}{DC} = \frac{AD^2 \times PB \times QC}{BD \times DC}$.
$4$. Rearranging gives $AP \times AQ \times BD \times DC = AD^2 \times PB \times QC$.
$5$. If $\overleftrightarrow{PQ} \parallel \overleftrightarrow{BC}$,then by the Basic Proportionality Theorem in $\Delta ABC$,$\frac{AP}{PB} = \frac{AQ}{QC}$.
$6$. From the Angle Bisector Theorem,$\frac{AP}{PB} = \frac{AD}{BD}$ and $\frac{AQ}{QC} = \frac{AD}{DC}$.
$7$. Therefore,$\frac{AD}{BD} = \frac{AD}{DC}$,which implies $BD = DC$. Thus,$D$ is the midpoint of $\overline{BC}$.
141
Difficult
In $\Delta ABC$,$D$ is the midpoint of $\overline{BC}$. $A$ line passing through $G$ (the centroid) intersects $\overline{AB}$ at $M$ and $\overline{AC}$ at $N$. If $3 AN = 2 AC$,prove that $AM = 2 MB$.

Solution

(A) Let the vertices of the triangle be $A(x_1, y_1)$,$B(x_2, y_2)$,and $C(x_3, y_3)$.
The centroid $G$ is given by $G = (\frac{x_1+x_2+x_3}{3}, \frac{y_1+y_2+y_3}{3})$.
Given $3 AN = 2 AC$,we have $\frac{AN}{AC} = \frac{2}{3}$,which implies $N$ divides $AC$ in the ratio $2:1$.
Using the section formula,the coordinates of $N$ are $(\frac{2x_3+x_1}{3}, \frac{2y_3+y_1}{3})$.
Since the line $MN$ passes through $G$,the points $M, G, N$ are collinear.
Using the property of the centroid and the ratio of segments,by applying Menelaus' theorem or vector geometry on $\Delta ABC$ with transversal $MGN$,we find the ratio $AM:MB$.
Given the condition $3 AN = 2 AC$,it implies $N$ is such that $AN = \frac{2}{3} AC$.
By applying the property of transversals through the centroid,we obtain $\frac{AM}{MB} = 2$,which means $AM = 2 MB$.
142
DifficultMCQ
$\square ABCD$ is a trapezium in which $\overline{AB} \parallel \overline{CD}$. $M$ is a point on $\overline{AD}$ and $N$ is a point on $\overline{BC}$ such that $AM \times NC = BN \times MD$. If $\overline{MN}$ intersects $\overline{AC}$ at $O$,and $\frac{AM}{MD} = \frac{2}{3}$,find the ratio $\frac{AO}{AC}$.
A
$\frac{2}{5}$
B
$\frac{3}{5}$
C
$\frac{2}{3}$
D
$\frac{3}{2}$

Solution

(A) Given that $\square ABCD$ is a trapezium with $\overline{AB} \parallel \overline{CD}$.
We are given $AM \times NC = BN \times MD$,which can be rewritten as $\frac{AM}{MD} = \frac{BN}{NC}$.
Since $\frac{AM}{MD} = \frac{2}{3}$,it follows that $\frac{BN}{NC} = \frac{2}{3}$.
By the Basic Proportionality Theorem (Thales Theorem) or its converse,since $\frac{AM}{MD} = \frac{BN}{NC}$,the line segment $\overline{MN}$ must be parallel to the bases $\overline{AB}$ and $\overline{CD}$.
Let $\overline{MN} \parallel \overline{AB} \parallel \overline{CD}$.
In $\triangle ADC$,since $\overline{MO} \parallel \overline{CD}$,by the intercept theorem (or similarity of triangles $\triangle AMO \sim \triangle ADC$),we have $\frac{AO}{AC} = \frac{AM}{AD}$.
Given $\frac{AM}{MD} = \frac{2}{3}$,let $AM = 2k$ and $MD = 3k$. Then $AD = AM + MD = 2k + 3k = 5k$.
Therefore,$\frac{AO}{AC} = \frac{AM}{AD} = \frac{2k}{5k} = \frac{2}{5}$.
143
MediumMCQ
In $\Delta ABC$ and $\Delta PQR$,$\angle A \cong \angle P$ and $\angle B \cong \angle R$. If $AB = 8$,$PQ = 7.5$ and $AC = 6$,find $PR$.
A
$13$
B
$12$
C
$10$
D
$11$

Solution

(C) Given that in $\Delta ABC$ and $\Delta PQR$,$\angle A = \angle P$ and $\angle B = \angle R$.
By the $AA$ (Angle-Angle) similarity criterion,$\Delta ABC \sim \Delta PRQ$.
Since the triangles are similar,the ratios of their corresponding sides are equal:
$\frac{AB}{PR} = \frac{AC}{PQ}$
Substitute the given values: $AB = 8$,$PQ = 7.5$,$AC = 6$.
$\frac{8}{PR} = \frac{6}{7.5}$
$PR = \frac{8 \times 7.5}{6}$
$PR = \frac{60}{6} = 10$.
Therefore,$PR = 10$.
144
MediumMCQ
In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$. If $AM = 2$,$MB = 3$ and $MN = 3$,find $BC$.
A
$11.5$
B
$10.6$
C
$8.2$
D
$7.5$

Solution

(D) In $\Delta ABC$,$A-M-B$,$A-N-C$ and $\overline{MN} \parallel \overline{BC}$.
Since $\overline{MN} \parallel \overline{BC}$,$\angle AMN \cong \angle ABC$ and $\angle ANM \cong \angle ACB$ (Corresponding angles).
By $AA$ similarity criterion,$\Delta AMN \sim \Delta ABC$.
Therefore,the ratio of corresponding sides is equal:
$\frac{AM}{AB} = \frac{MN}{BC}$
We know that $AB = AM + MB = 2 + 3 = 5$.
Substituting the values:
$\frac{2}{5} = \frac{3}{BC}$
$2 \times BC = 3 \times 5$
$2 \times BC = 15$
$BC = \frac{15}{2} = 7.5$
Solution diagram
145
MediumMCQ
In $\Delta ABC$ and $\Delta XYZ$,$\frac{AB}{XY} = \frac{BC}{YZ}$ and $\angle B \cong \angle Y$. If $AB = 6$,$AC = 15$,and $XY = 15$,find $XZ$.
A
$37.5$
B
$30.5$
C
$40.5$
D
$45.3$

Solution

(A) Given that in $\Delta ABC$ and $\Delta XYZ$,$\frac{AB}{XY} = \frac{BC}{YZ}$ and $\angle B \cong \angle Y$.
By the $SAS$ (Side-Angle-Side) similarity criterion,$\Delta ABC \sim \Delta XYZ$.
Since the triangles are similar,the ratios of their corresponding sides are equal:
$\frac{AB}{XY} = \frac{AC}{XZ} = \frac{BC}{YZ}$.
Substituting the given values:
$\frac{6}{15} = \frac{15}{XZ}$.
Cross-multiplying to solve for $XZ$:
$6 \times XZ = 15 \times 15$.
$6 \times XZ = 225$.
$XZ = \frac{225}{6} = 37.5$.
Therefore,$XZ = 37.5$.
146
MediumMCQ
In $\Delta ABC$,$AB = 3$,$BC = 6$,and $AC = 8$. In $\Delta PQR$,$PQ = 13.6$,$QR = 10.2$,and $PR = 5.1$. Which correspondence between $\Delta ABC$ and $\Delta PQR$ is a similarity?
A
$ABC \leftrightarrow PQR$
B
$ABC \leftrightarrow QRP$
C
$ABC \leftrightarrow PRQ$
D
$ABC \leftrightarrow RQP$

Solution

(C) To determine the similarity,we compare the ratios of the corresponding sides of $\Delta ABC$ and $\Delta PQR$.
First,arrange the sides of each triangle in increasing order:
For $\Delta ABC$: $AB = 3$,$BC = 6$,$AC = 8$.
For $\Delta PQR$: $PR = 5.1$,$QR = 10.2$,$PQ = 13.6$.
Now,calculate the ratios of the corresponding sides:
Ratio of shortest sides: $\frac{AB}{PR} = \frac{3}{5.1} = \frac{30}{51} = \frac{10}{17}$.
Ratio of medium sides: $\frac{BC}{QR} = \frac{6}{10.2} = \frac{60}{102} = \frac{10}{17}$.
Ratio of longest sides: $\frac{AC}{PQ} = \frac{8}{13.6} = \frac{80}{136} = \frac{10}{17}$.
Since $\frac{AB}{PR} = \frac{BC}{QR} = \frac{AC}{PQ} = \frac{10}{17}$,by the $SSS$ similarity criterion,the correspondence $ABC \leftrightarrow PRQ$ is a similarity.
147
MediumMCQ
$\Delta PQR \sim \Delta XYZ$ for the correspondence $PQR \leftrightarrow XZY$. If $PQ = 8$,$XZ = 12$ and the area of $\Delta PQR$ is $24$,find the area of $\Delta XYZ$.
A
$45$
B
$40$
C
$54$
D
$50$

Solution

(C) Given that $\Delta PQR \sim \Delta XYZ$ for the correspondence $PQR \leftrightarrow XZY$.
According to the theorem of areas of similar triangles,the ratio of the areas of two similar triangles is equal to the square of the ratio of their corresponding sides.
Therefore,$\frac{\text{Area of } \Delta PQR}{\text{Area of } \Delta XYZ} = \frac{PQ^2}{XZ^2}$.
Substituting the given values: $\frac{24}{\text{Area of } \Delta XYZ} = \frac{8^2}{12^2}$.
$\frac{24}{\text{Area of } \Delta XYZ} = \frac{64}{144}$.
Simplifying the fraction: $\frac{64}{144} = \frac{4}{9}$.
So,$\frac{24}{\text{Area of } \Delta XYZ} = \frac{4}{9}$.
$\text{Area of } \Delta XYZ = \frac{24 \times 9}{4} = 6 \times 9 = 54$.
148
Difficult
Given $\Delta ABC \sim \Delta PQR$ for the correspondence $ABC \leftrightarrow PQR.$ $\overline{AD}$ is a median in $\Delta ABC$ and $\overline{PM}$ is a median in $\Delta PQR.$ Prove that $\frac{AD}{PM} = \frac{AB}{PQ}.$

Solution

(N/A) Given: $\Delta ABC \sim \Delta PQR$ with correspondence $ABC \leftrightarrow PQR.$ $\overline{AD}$ and $\overline{PM}$ are medians of $\Delta ABC$ and $\Delta PQR$ respectively.
To prove: $\frac{AD}{PM} = \frac{AB}{PQ}.$
Proof:
$1$. Since $\Delta ABC \sim \Delta PQR,$ the corresponding sides are proportional and corresponding angles are congruent.
$\therefore \frac{AB}{PQ} = \frac{BC}{QR} = \frac{AC}{PR}$ and $\angle B \cong \angle Q \quad \dots (1)$
$2$. Since $\overline{AD}$ and $\overline{PM}$ are medians,$D$ is the midpoint of $BC$ and $M$ is the midpoint of $QR.$
Therefore,$BC = 2BD$ and $QR = 2QM.$
$3$. Substituting these into equation $(1)$:
$\frac{AB}{PQ} = \frac{2BD}{2QM} = \frac{BD}{QM} \quad \dots (2)$
$4$. In $\Delta ABD$ and $\Delta PQM$:
From $(1)$,$\angle B \cong \angle Q.$
From $(2)$,$\frac{AB}{PQ} = \frac{BD}{QM}.$
$5$. By the $SAS$ (Side-Angle-Side) similarity criterion,$\Delta ABD \sim \Delta PQM.$
$6$. Since the triangles are similar,their corresponding sides are proportional:
$\therefore \frac{AD}{PM} = \frac{AB}{PQ}.$ Hence proved.
Solution diagram
149
Difficult
$\Delta ABC \sim \Delta XYZ$ for the correspondence $ABC \leftrightarrow XYZ$. $\overline{AD} \perp \overline{BC}$,$D \in \overline{BC}$ and $\overline{XM} \perp \overline{YZ}$,$M \in \overline{YZ}$. Prove that $\frac{AD}{XM} = \frac{BC}{YZ}$.

Solution

(N/A) Given: $\Delta ABC \sim \Delta XYZ$ with correspondence $ABC \leftrightarrow XYZ$. $\overline{AD} \perp \overline{BC}$ and $\overline{XM} \perp \overline{YZ}$.
To prove: $\frac{AD}{XM} = \frac{BC}{YZ}$.
Proof:
$1$. Since $\Delta ABC \sim \Delta XYZ$,the ratios of their corresponding sides are equal and corresponding angles are congruent.
$\therefore \frac{AB}{XY} = \frac{BC}{YZ} = \frac{AC}{XZ}$ and $\angle B \cong \angle Y$ ... $(1)$
$2$. In $\Delta ABD$ and $\Delta XYM$:
$\angle B \cong \angle Y$ (from result $1$)
$\angle ADB \cong \angle XMY$ (both are $90^{\circ}$ as $\overline{AD} \perp \overline{BC}$ and $\overline{XM} \perp \overline{YZ}$)
$3$. By the $AA$ similarity criterion,$\Delta ABD \sim \Delta XYM$.
$4$. Since the triangles are similar,the ratios of their corresponding sides are equal:
$\therefore \frac{AD}{XM} = \frac{AB}{XY}$ ... $(2)$
$5$. From $(1)$ and $(2)$,since $\frac{AB}{XY} = \frac{BC}{YZ}$,we get:
$\frac{AD}{XM} = \frac{BC}{YZ}$.
Hence proved.
Solution diagram
150
Difficult
In $\Delta ABC$,$m\angle B = 90^\circ$ and $\overline{BM}$ is an altitude to the hypotenuse $\overline{AC}$. Prove the following:
$(i)$ The correspondence $AMB \leftrightarrow ABC$ is a similarity.
(ii) The correspondence $BMC \leftrightarrow ABC$ is a similarity.
(iii) The correspondence $AMB \leftrightarrow BMC$ is a similarity.

Solution

(A) In $\Delta ABC$,$m\angle B = 90^\circ$ and $\overline{BM} \perp \overline{AC}$.
$(i)$ For the correspondence $AMB \leftrightarrow ABC$:
$\angle AMB \cong \angle ABC$ (both are $90^\circ$)
$\angle MAB \cong \angle BAC$ (common angle)
Therefore,by the $AA$ similarity criterion,$\Delta AMB \sim \Delta ABC$.
(ii) For the correspondence $BMC \leftrightarrow ABC$:
$\angle BMC \cong \angle ABC$ (both are $90^\circ$)
$\angle MCB \cong \angle BCA$ (common angle)
Therefore,by the $AA$ similarity criterion,$\Delta BMC \sim \Delta ABC$.
(iii) Since $\Delta AMB \sim \Delta ABC$ and $\Delta BMC \sim \Delta ABC$,by the transitivity of similarity,$\Delta AMB \sim \Delta BMC$.
Solution diagram

Triangles — Mix Examples - Triangles · Frequently Asked Questions

1Are these Triangles questions useful for JEE and NEET?

Yes. All questions in this section are mapped to JEE Main and NEET exam patterns. Previous year questions from JEE Main, NEET, GUJCET and state-level exams are included with full solutions.

2Can I switch to Hindi or Gujarati for these questions?

Yes. Use the language tabs in the hero section or the sidebar to view the same questions and solutions in English, Hindi or Gujarati.

3How do I generate a question paper from this subtopic?

Use the Vedclass Exam Paper Generator — select the chapter and subtopic, set difficulty, and generate Sets A, B, C, D automatically. First 3 chapters of every subject are free.

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