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Relation between roots and coefficients Questions in English

Class 11 Mathematics · 4-2.Quadratic Equations and Inequations · Relation between roots and coefficients

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451
MediumMCQ
$\alpha, \beta, \gamma$ are the roots of the equation $8x^3 - 42x^2 + 63x - 27 = 0$. If $\beta < \gamma < \alpha$ and $\beta, \gamma, \alpha$ are in geometric progression,then the extreme value of the expression $\gamma x^2 + 4\beta x + \alpha$ is
A
$\frac{3}{4}$
B
$3$
C
$\frac{3}{2}$
D
$\frac{21}{4}$

Solution

(C) Given equation: $8x^3 - 42x^2 + 63x - 27 = 0$ . . . $(i)$
Since $\alpha, \beta, \gamma$ are roots of $(i)$,the product of roots is $\alpha \beta \gamma = -(\frac{-27}{8}) = \frac{27}{8}$.
Given $\beta, \gamma, \alpha$ are in geometric progression,so $\gamma^2 = \beta \alpha$.
Substituting this into the product of roots: $\gamma \cdot \gamma^2 = \frac{27}{8} \implies \gamma^3 = \frac{27}{8} \implies \gamma = \frac{3}{2}$.
Sum of roots: $\alpha + \beta + \gamma = \frac{42}{8} = \frac{21}{4}$.
Since $\alpha + \beta = \frac{21}{4} - \frac{3}{2} = \frac{15}{4}$ and $\alpha \beta = \gamma^2 = \frac{9}{4}$,$\alpha$ and $\beta$ are roots of $t^2 - \frac{15}{4}t + \frac{9}{4} = 0 \implies 4t^2 - 15t + 9 = 0 \implies (4t - 3)(t - 3) = 0$.
Thus,$t = \frac{3}{4}$ or $t = 3$. Given $\beta < \gamma < \alpha$,we have $\beta = \frac{3}{4}, \gamma = \frac{3}{2}, \alpha = 3$.
The expression is $\frac{3}{2}x^2 + 4(\frac{3}{4})x + 3 = \frac{3}{2}x^2 + 3x + 3$.
The extreme value of $ax^2 + bx + c$ is $-\frac{D}{4a} = \frac{4ac - b^2}{4a}$.
Here $a = \frac{3}{2}, b = 3, c = 3$,so the extreme value is $\frac{4(\frac{3}{2})(3) - (3)^2}{4(\frac{3}{2})} = \frac{18 - 9}{6} = \frac{9}{6} = \frac{3}{2}$.
452
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $4x^3-3x^2+2x-1=0$,then $\alpha^3+\beta^3+\gamma^3=$
A
$\frac{2}{27}$
B
$\frac{1}{8}$
C
$\frac{3}{64}$
D
$\frac{27}{128}$

Solution

(C) Given that $\alpha, \beta, \gamma$ are the roots of the equation $4x^3-3x^2+2x-1=0$.
Since they are roots,they satisfy the equation:
$4\alpha^3-3\alpha^2+2\alpha-1=0 \Rightarrow 4\alpha^3=3\alpha^2-2\alpha+1$
$4\beta^3-3\beta^2+2\beta-1=0 \Rightarrow 4\beta^3=3\beta^2-2\beta+1$
$4\gamma^3-3\gamma^2+2\gamma-1=0 \Rightarrow 4\gamma^3=3\gamma^2-2\gamma+1$
Summing these equations:
$4(\alpha^3+\beta^3+\gamma^3) = 3(\alpha^2+\beta^2+\gamma^2) - 2(\alpha+\beta+\gamma) + 3$
From Vieta's formulas:
$\alpha+\beta+\gamma = \frac{3}{4}$,$\alpha\beta+\beta\gamma+\gamma\alpha = \frac{2}{4} = \frac{1}{2}$,$\alpha\beta\gamma = \frac{1}{4}$
We know $\alpha^2+\beta^2+\gamma^2 = (\alpha+\beta+\gamma)^2 - 2(\alpha\beta+\beta\gamma+\gamma\alpha) = (\frac{3}{4})^2 - 2(\frac{1}{2}) = \frac{9}{16} - 1 = -\frac{7}{16}$
Substituting these values:
$4(\alpha^3+\beta^3+\gamma^3) = 3(-\frac{7}{16}) - 2(\frac{3}{4}) + 3 = -\frac{21}{16} - \frac{3}{2} + 3 = -\frac{21}{16} + \frac{3}{2} = \frac{-21+24}{16} = \frac{3}{16}$
Therefore,$\alpha^3+\beta^3+\gamma^3 = \frac{3}{64}$.
453
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3-3x^2+3x+1=0$,then $\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2=$
A
$9$
B
$15$
C
$8$
D
$20$

Solution

(B) Given the cubic equation $x^3-3x^2+3x+1=0$.
By Vieta's formulas,we have:
$\alpha+\beta+\gamma = 3$
$\alpha\beta+\beta\gamma+\gamma\alpha = 3$
$\alpha\beta\gamma = -1$
We need to find $\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2$.
Using the identity $(a+b+c)^2 = a^2+b^2+c^2+2(ab+bc+ca)$,let $a=\alpha\beta, b=\beta\gamma, c=\gamma\alpha$.
Then $(\alpha\beta+\beta\gamma+\gamma\alpha)^2 = \alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 + 2(\alpha\beta^2\gamma + \beta\gamma^2\alpha + \gamma\alpha^2\beta)$.
Factor out $\alpha\beta\gamma$ from the second term:
$\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 = (\alpha\beta+\beta\gamma+\gamma\alpha)^2 - 2\alpha\beta\gamma(\beta+\alpha+\gamma)$.
Substitute the known values:
$\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 = (3)^2 - 2(-1)(3) = 9 + 6 = 15$.
454
EasyMCQ
If $\alpha, \beta, \gamma$ are the real roots of the equation $18x^3-15x^2-4x+4=0$ such that $\alpha=\beta$ and $\alpha>\gamma$,then $\alpha+\beta^2+\gamma^3=$
A
$\frac{71}{72}$
B
$\frac{53}{54}$
C
$\frac{89}{90}$
D
$\frac{59}{60}$

Solution

(A) Given the equation $18x^3-15x^2-4x+4=0$.
Let the roots be $\alpha, \alpha, \gamma$ where $\alpha > \gamma$.
From Vieta's formulas:
$2\alpha + \gamma = \frac{15}{18} = \frac{5}{6}$ $(i)$
$\alpha^2 + 2\alpha\gamma = \frac{-4}{18} = -\frac{2}{9}$ (ii)
$\alpha^2\gamma = -\frac{4}{18} = -\frac{2}{9}$ (iii)
From (ii) and (iii),$\alpha^2 + 2\alpha\gamma = \alpha^2\gamma$.
Since $\alpha \neq 0$,we have $\alpha + 2\gamma = \alpha\gamma$.
From $(i)$,$\gamma = \frac{5}{6} - 2\alpha$.
Substituting into $\alpha + 2\gamma = \alpha\gamma$:
$\alpha + 2(\frac{5}{6} - 2\alpha) = \alpha(\frac{5}{6} - 2\alpha)$
$\alpha + \frac{5}{3} - 4\alpha = \frac{5\alpha}{6} - 2\alpha^2$
$2\alpha^2 - 3\alpha + \frac{5}{3} = \frac{5\alpha}{6}$
$12\alpha^2 - 18\alpha + 10 = 5\alpha$
$12\alpha^2 - 23\alpha + 10 = 0$
$(3\alpha - 2)(4\alpha - 5) = 0$.
So,$\alpha = \frac{2}{3}$ or $\alpha = \frac{5}{4}$.
If $\alpha = \frac{2}{3}$,then $\gamma = \frac{5}{6} - 2(\frac{2}{3}) = \frac{5}{6} - \frac{4}{3} = -\frac{1}{2}$.
Since $\alpha > \gamma$ $(\frac{2}{3} > -\frac{1}{2})$,this is a valid solution.
Then $\alpha + \beta^2 + \gamma^3 = \frac{2}{3} + (\frac{2}{3})^2 + (-\frac{1}{2})^3 = \frac{2}{3} + \frac{4}{9} - \frac{1}{8} = \frac{48 + 32 - 9}{72} = \frac{71}{72}$.
455
EasyMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $2x^3+x^2-13x+6=0$,then $\alpha^3+\beta^3+\gamma^3=$
A
$-\frac{161}{8}$
B
$36$
C
$99$
D
$-\frac{151}{8}$

Solution

(D) Given the cubic equation $2x^3+x^2-13x+6=0$.
By Vieta's formulas,for roots $\alpha, \beta, \gamma$:
$\alpha+\beta+\gamma = -\frac{1}{2}$
$\alpha\beta+\beta\gamma+\gamma\alpha = -\frac{13}{2}$
$\alpha\beta\gamma = -\frac{6}{2} = -3$
We use the identity: $\alpha^3+\beta^3+\gamma^3 - 3\alpha\beta\gamma = (\alpha+\beta+\gamma)(\alpha^2+\beta^2+\gamma^2 - (\alpha\beta+\beta\gamma+\gamma\alpha))$
Note that $\alpha^2+\beta^2+\gamma^2 = (\alpha+\beta+\gamma)^2 - 2(\alpha\beta+\beta\gamma+\gamma\alpha) = (-\frac{1}{2})^2 - 2(-\frac{13}{2}) = \frac{1}{4} + 13 = \frac{53}{4}$.
Substituting these values:
$\alpha^3+\beta^3+\gamma^3 = (\alpha+\beta+\gamma)(\frac{53}{4} - (-\frac{13}{2})) + 3(-3)$
$= (-\frac{1}{2})(\frac{53}{4} + \frac{26}{4}) - 9$
$= (-\frac{1}{2})(\frac{79}{4}) - 9$
$= -\frac{79}{8} - \frac{72}{8} = -\frac{151}{8}$.
456
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3 + x^2 + x + 1 = 0$,then match the items of List-$I$ with those of List-$II$:
List-$I$:
$(i)$ $\frac{1}{\alpha} + \frac{1}{\beta} + \frac{1}{\gamma}$
(ii) $\alpha^3 + \beta^3 + \gamma^3$
(iii) $\alpha^4 + \beta^4 + \gamma^4$
(iv) $(\alpha - \beta)^2 + (\beta - \gamma)^2 + (\gamma - \alpha)^2$
List-$II$:
$(A)$ $-1$
$(B)$ $-4$
$(C)$ $1$
$(D)$ $3$
$(E)$ $0$
A
$(i)$ $\rightarrow$ $A$,(ii) $\rightarrow$ $A$,(iii) $\rightarrow$ $D$,(iv) $\rightarrow$ $B$
B
$(i)$ $\rightarrow$ $C$,(ii) $\rightarrow$ $A$,(iii) $\rightarrow$ $E$,(iv) $\rightarrow$ $B$
C
$(i)$ $\rightarrow$ $A$,(ii) $\rightarrow$ $C$,(iii) $\rightarrow$ $D$,(iv) $\rightarrow$ $B$
D
$(i)$ $\rightarrow$ $C$,(ii) $\rightarrow$ $A$,(iii) $\rightarrow$ $B$,(iv) $\rightarrow$ $E$

Solution

(A) Given the equation $x^3 + x^2 + x + 1 = 0$,the roots are $\alpha, \beta, \gamma$.
By Vieta's formulas:
$\alpha + \beta + \gamma = -1$
$\alpha \beta + \beta \gamma + \gamma \alpha = 1$
$\alpha \beta \gamma = -1$
$(i)$ $\frac{1}{\alpha} + \frac{1}{\beta} + \frac{1}{\gamma} = \frac{\alpha \beta + \beta \gamma + \gamma \alpha}{\alpha \beta \gamma} = \frac{1}{-1} = -1$. Thus,$(i)$ $\rightarrow$ $A$.
(ii) $\alpha^3 + \beta^3 + \gamma^3$: Since $\alpha, \beta, \gamma$ are roots,$\alpha^3 = -\alpha^2 - \alpha - 1$,$\beta^3 = -\beta^2 - \beta - 1$,$\gamma^3 = -\gamma^2 - \gamma - 1$.
Summing these: $\alpha^3 + \beta^3 + \gamma^3 = -(\alpha^2 + \beta^2 + \gamma^2) - (\alpha + \beta + \gamma) - 3$.
We know $\alpha^2 + \beta^2 + \gamma^2 = (\alpha + \beta + \gamma)^2 - 2(\alpha \beta + \beta \gamma + \gamma \alpha) = (-1)^2 - 2(1) = 1 - 2 = -1$.
So,$\alpha^3 + \beta^3 + \gamma^3 = -(-1) - (-1) - 3 = 1 + 1 - 3 = -1$. Thus,(ii) $\rightarrow$ $A$.
(iii) $\alpha^4 + \beta^4 + \gamma^4$: Multiply the original equation by $x$: $x^4 + x^3 + x^2 + x = 0$.
Summing for roots: $(\alpha^4 + \beta^4 + \gamma^4) + (\alpha^3 + \beta^3 + \gamma^3) + (\alpha^2 + \beta^2 + \gamma^2) + (\alpha + \beta + \gamma) = 0$.
$(\alpha^4 + \beta^4 + \gamma^4) + (-1) + (-1) + (-1) = 0 \Rightarrow \alpha^4 + \beta^4 + \gamma^4 = 3$. Thus,(iii) $\rightarrow$ $D$.
(iv) $(\alpha - \beta)^2 + (\beta - \gamma)^2 + (\gamma - \alpha)^2 = 2(\alpha^2 + \beta^2 + \gamma^2) - 2(\alpha \beta + \beta \gamma + \gamma \alpha) = 2(-1) - 2(1) = -2 - 2 = -4$. Thus,(iv) $\rightarrow$ $B$.
The correct match is $(i)$ $\rightarrow$ $A$,(ii) $\rightarrow$ $A$,(iii) $\rightarrow$ $D$,(iv) $\rightarrow$ $B$.
457
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3+x^2+x+r=0$ and $\alpha^3+\beta^3+\gamma^3=5$,then $r=$
A
$\frac{-1}{2}$
B
$1$
C
$-1$
D
$\frac{1}{2}$

Solution

(C) Given that $\alpha, \beta, \gamma$ are the roots of the equation $x^3+x^2+x+r=0$.
From Vieta's formulas:
$\alpha+\beta+\gamma = -1$
$\alpha\beta+\beta\gamma+\gamma\alpha = 1$
$\alpha\beta\gamma = -r$
We use the identity:
$\alpha^3+\beta^3+\gamma^3-3\alpha\beta\gamma = (\alpha+\beta+\gamma)(\alpha^2+\beta^2+\gamma^2-\alpha\beta-\beta\gamma-\gamma\alpha)$
Note that $\alpha^2+\beta^2+\gamma^2 = (\alpha+\beta+\gamma)^2 - 2(\alpha\beta+\beta\gamma+\gamma\alpha) = (-1)^2 - 2(1) = 1-2 = -1$.
Substituting the values into the identity:
$5 - 3(-r) = (-1)(-1 - 1)$
$5 + 3r = (-1)(-2)$
$5 + 3r = 2$
$3r = 2 - 5$
$3r = -3$
$r = -1$
458
MediumMCQ
If $\alpha, \beta, 2 \beta$ are the real roots of the equation $x^3-9 x^2+k=0$ and $k \in R-\{0\}$,then $14 \beta=$
A
$28$
B
$36$
C
$18$
D
$54$

Solution

(D) Given the cubic equation $x^3-9 x^2+k=0$,where the roots are $\alpha, \beta, 2 \beta$.
Using Vieta's formulas:
Sum of roots: $\alpha + \beta + 2 \beta = 9 \implies \alpha + 3 \beta = 9$ $(i)$
Sum of roots taken two at a time: $\alpha \beta + \beta(2 \beta) + 2 \beta(\alpha) = 0$ (since the coefficient of $x$ is $0$)
$\alpha \beta + 2 \beta^2 + 2 \alpha \beta = 0 \implies 3 \alpha \beta + 2 \beta^2 = 0$
$\beta(3 \alpha + 2 \beta) = 0$
Since $k \neq 0$,the product of roots $\alpha \cdot \beta \cdot 2 \beta = -k \neq 0$,so $\beta \neq 0$.
Thus,$3 \alpha + 2 \beta = 0 \implies \alpha = -\frac{2 \beta}{3}$ $(ii)$
Substitute $(ii)$ into $(i)$:
$-\frac{2 \beta}{3} + 3 \beta = 9$
$\frac{-2 \beta + 9 \beta}{3} = 9$
$\frac{7 \beta}{3} = 9 \implies 7 \beta = 27$
Therefore,$14 \beta = 2 \times (7 \beta) = 2 \times 27 = 54$.
Thus,the correct option is $(d)$.
459
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3-9x^2+23x-15=0$,then $\alpha^3+\beta^3+\gamma^3=$
A
$36$
B
$92$
C
$153$
D
$244$

Solution

(C) Given the cubic equation $x^3-9x^2+23x-15=0$.
By Vieta's formulas,for roots $\alpha, \beta, \gamma$:
$\alpha+\beta+\gamma = 9$ ... $(i)$
$\alpha\beta+\beta\gamma+\gamma\alpha = 23$ ... (ii)
$\alpha\beta\gamma = 15$ ... (iii)
Since $\alpha, \beta, \gamma$ are roots,they satisfy the equation:
$\alpha^3-9\alpha^2+23\alpha-15=0 \implies \alpha^3 = 9\alpha^2-23\alpha+15$
$\beta^3-9\beta^2+23\beta-15=0 \implies \beta^3 = 9\beta^2-23\beta+15$
$\gamma^3-9\gamma^2+23\gamma-15=0 \implies \gamma^3 = 9\gamma^2-23\gamma+15$
Adding these three equations:
$\alpha^3+\beta^3+\gamma^3 = 9(\alpha^2+\beta^2+\gamma^2) - 23(\alpha+\beta+\gamma) + 45$
We know $\alpha^2+\beta^2+\gamma^2 = (\alpha+\beta+\gamma)^2 - 2(\alpha\beta+\beta\gamma+\gamma\alpha) = 9^2 - 2(23) = 81 - 46 = 35$.
Substituting the values:
$\alpha^3+\beta^3+\gamma^3 = 9(35) - 23(9) + 45$
$= 315 - 207 + 45 = 153$.
Thus,the correct option is $C$.
460
EasyMCQ
If $\alpha, \beta, \gamma$ are the roots of $x^3-x+1=0$,then $\frac{1+\alpha}{1-\alpha}+\frac{1+\beta}{1-\beta}+\frac{1+\gamma}{1-\gamma}=$
A
$1$
B
$0$
C
$2$
D
$-2$

Solution

(A) Given the cubic equation $x^3-x+1=0$.
Let $f(x) = x^3-x+1$.
By Vieta's formulas,for roots $\alpha, \beta, \gamma$:
$\alpha+\beta+\gamma = 0$
$\alpha\beta+\beta\gamma+\gamma\alpha = -1$
$\alpha\beta\gamma = -1$
Let $y = \frac{1+x}{1-x}$. Then $y(1-x) = 1+x \implies y-yx = 1+x \implies y-1 = x(1+y) \implies x = \frac{y-1}{y+1}$.
Since $x$ is a root of $x^3-x+1=0$,we substitute $x = \frac{y-1}{y+1}$:
$(\frac{y-1}{y+1})^3 - (\frac{y-1}{y+1}) + 1 = 0$
$(y-1)^3 - (y-1)(y+1)^2 + (y+1)^3 = 0$
$(y^3-3y^2+3y-1) - (y-1)(y^2+2y+1) + (y^3+3y^2+3y+1) = 0$
$(y^3-3y^2+3y-1) - (y^3+2y^2+y-y^2-2y-1) + (y^3+3y^2+3y+1) = 0$
$y^3-3y^2+3y-1 - y^3-y^2+y+1 + y^3+3y^2+3y+1 = 0$
$y^3-y^2+7y+1 = 0$
The roots of this equation are $y_1 = \frac{1+\alpha}{1-\alpha}, y_2 = \frac{1+\beta}{1-\beta}, y_3 = \frac{1+\gamma}{1-\gamma}$.
The sum of the roots is $y_1+y_2+y_3 = -(\frac{-1}{1}) = 1$.
461
EasyMCQ
If $x^2-3x+2$ is a factor of $x^4-ax^2+b$,then the equation whose roots are $a$ and $b$ is
A
$x^2-9x-20=0$
B
$x^2-9x+20=0$
C
$x^2+9x-20=0$
D
$x^2+9x+20=0$

Solution

(B) Given that $x^2-3x+2$ is a factor of $P(x) = x^4-ax^2+b$.
Factorizing the divisor: $x^2-3x+2 = (x-1)(x-2)$.
Since $(x-1)$ and $(x-2)$ are factors,$P(1) = 0$ and $P(2) = 0$.
For $x=1$: $(1)^4 - a(1)^2 + b = 0 \implies 1 - a + b = 0 \implies -a + b = -1$ (Equation $i$).
For $x=2$: $(2)^4 - a(2)^2 + b = 0 \implies 16 - 4a + b = 0 \implies -4a + b = -16$ (Equation $ii$).
Subtracting (Equation $ii$) from (Equation $i$): $(-a+b) - (-4a+b) = -1 - (-16) \implies 3a = 15 \implies a = 5$.
Substituting $a=5$ into (Equation $i$): $-5 + b = -1 \implies b = 4$.
The roots of the required quadratic equation are $a=5$ and $b=4$.
The equation is given by $x^2 - (a+b)x + ab = 0$.
Substituting the values: $x^2 - (5+4)x + (5 \times 4) = 0 \implies x^2 - 9x + 20 = 0$.
462
EasyMCQ
If $2$ and $3$ are two roots of the equation $2x^3 + mx^2 - 13x + n = 0$,then the values of $m$ and $n$ are respectively
A
$-5, -30$
B
$-5, 30$
C
$5, 30$
D
$5, -30$

Solution

(B) Given the equation $2x^3 + mx^2 - 13x + n = 0$. Since $2$ and $3$ are roots,they must satisfy the equation.
For $x = 2$:
$2(2)^3 + m(2)^2 - 13(2) + n = 0$
$16 + 4m - 26 + n = 0$
$4m + n = 10$ --- $(i)$
For $x = 3$:
$2(3)^3 + m(3)^2 - 13(3) + n = 0$
$54 + 9m - 39 + n = 0$
$9m + n = -15$ --- $(ii)$
Subtracting $(i)$ from $(ii)$:
$(9m + n) - (4m + n) = -15 - 10$
$5m = -25 \Rightarrow m = -5$
Substituting $m = -5$ in $(i)$:
$4(-5) + n = 10$
$-20 + n = 10 \Rightarrow n = 30$
Thus,the values are $m = -5$ and $n = 30$.
463
MediumMCQ
For the equation $x^4+x^3-4x^2+x-1=0$,the ratio of the sum of the squares of all the roots to the product of the distinct roots is
A
$1: 4$
B
$3: 5$
C
$9: 1$
D
$4: 3$

Solution

(C) Given equation: $x^4+x^3-4x^2+x-1=0$.
Factoring the polynomial: $x^4-1+x^3+x-4x^2 = (x^2-1)(x^2+1)+x(x^2+1)-4x^2 = (x^2+1)(x^2-1+x)-4x^2 = (x^2+1)(x^2+x-1)-4x^2$.
Alternatively,notice $x=1$ is a root: $(x-1)(x^3+2x^2-2x+1)=0$.
Further factoring: $(x-1)(x+1)(x^2+x-1)=0$.
The roots are $x_1=1, x_2=-1, x_3=\frac{-1+\sqrt{5}}{2}, x_4=\frac{-1-\sqrt{5}}{2}$.
Sum of squares of roots: $\sum x_i^2 = (1)^2+(-1)^2+(\frac{-1+\sqrt{5}}{2})^2+(\frac{-1-\sqrt{5}}{2})^2 = 1+1+\frac{1-2\sqrt{5}+5}{4}+\frac{1+2\sqrt{5}+5}{4} = 2+\frac{6}{4}+\frac{6}{4} = 2+3 = 5$.
Distinct roots are $1, -1, \frac{-1+\sqrt{5}}{2}, \frac{-1-\sqrt{5}}{2}$.
Product of distinct roots: $1 \times (-1) \times (\frac{-1+\sqrt{5}}{2} \times \frac{-1-\sqrt{5}}{2}) = -1 \times (\frac{1-5}{4}) = -1 \times (-1) = 1$.
Ratio: $5:1$.
Wait,re-evaluating the polynomial $x^4+x^3-4x^2+x-1=0$.
Sum of squares $\sum x_i^2 = (\sum x_i)^2 - 2\sum x_ix_j = (-1)^2 - 2(-4) = 1+8 = 9$.
Product of distinct roots: $1 \times (-1) \times (-1) = 1$.
Ratio is $9:1$.
464
EasyMCQ
$p$ is a non-zero real number. If the equation whose roots are the squares of the roots of the equation $x^3 - px^2 + px - 1 = 0$ is identical to the given equation,then $p =$
A
$1/2$
B
$2$
C
$3$
D
$-1$

Solution

(C) Let $\alpha, \beta, \gamma$ be the roots of the equation $x^3 - px^2 + px - 1 = 0$.
From Vieta's formulas:
$\alpha + \beta + \gamma = p$
$\alpha\beta + \beta\gamma + \gamma\alpha = p$
$\alpha\beta\gamma = 1$
Given that the equation with roots $\alpha^2, \beta^2, \gamma^2$ is identical to the original equation,the sum of these roots must also be $p$:
$\alpha^2 + \beta^2 + \gamma^2 = p$
We know that $(\alpha + \beta + \gamma)^2 = \alpha^2 + \beta^2 + \gamma^2 + 2(\alpha\beta + \beta\gamma + \gamma\alpha)$.
Substituting the known values:
$p^2 = p + 2(p)$
$p^2 = 3p$
Since $p$ is non-zero,we divide by $p$:
$p = 3$.
465
EasyMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3+p x^2+q x+r=0$,then $(\alpha+\beta)(\beta+\gamma)(\gamma+\alpha) =$
A
$p-qr$
B
$r-pq$
C
$q-rp$
D
$r+pq$

Solution

(B) Given the cubic equation $x^3+px^2+qx+r=0$ with roots $\alpha, \beta, \gamma$.
By Vieta's formulas:
$\alpha+\beta+\gamma = -p$
$\alpha\beta+\beta\gamma+\gamma\alpha = q$
$\alpha\beta\gamma = -r$
We know that $(\alpha+\beta+\gamma)(\alpha\beta+\beta\gamma+\gamma\alpha) = (\alpha+\beta)(\beta+\gamma)(\gamma+\alpha) + \alpha\beta\gamma$.
Substituting the values:
$(-p)(q) = (\alpha+\beta)(\beta+\gamma)(\gamma+\alpha) + (-r)$
$-pq = (\alpha+\beta)(\beta+\gamma)(\gamma+\alpha) - r$
Therefore,$(\alpha+\beta)(\beta+\gamma)(\gamma+\alpha) = r-pq$.
466
DifficultMCQ
If $\alpha, \beta, \gamma$ are the roots of the cubic equation $x^3+p_1 x^2+p_2 x+p_3=0$. Let $S_r=\alpha^r+\beta^r+\gamma^r$. Given $S_1=10, S_2=38$ and $S_3=-1840$,then $p_3=$
A
-$30$
B
$\frac{1910}{3}$
C
$631$
D
-$31$

Solution

(B) Given that $\alpha, \beta, \gamma$ are the roots of $x^3+p_1 x^2+p_2 x+p_3=0$.
By Vieta's formulas,$p_1 = -(\alpha+\beta+\gamma) = -S_1 = -10$.
$p_2 = \alpha\beta+\beta\gamma+\gamma\alpha = \frac{(\alpha+\beta+\gamma)^2 - (\alpha^2+\beta^2+\gamma^2)}{2} = \frac{S_1^2 - S_2}{2} = \frac{100-38}{2} = 31$.
Using the identity $\alpha^3+\beta^3+\gamma^3 - 3\alpha\beta\gamma = (\alpha+\beta+\gamma)(\alpha^2+\beta^2+\gamma^2 - (\alpha\beta+\beta\gamma+\gamma\alpha))$,we have:
$S_3 - 3(-p_3) = S_1(S_2 - p_2)$.
$-1840 + 3p_3 = 10(38 - 31)$.
$-1840 + 3p_3 = 10(7) = 70$.
$3p_3 = 1910$.
$p_3 = \frac{1910}{3}$.
467
EasyMCQ
If $\alpha, \beta, \gamma$ are the roots of $x^3+p x^2+q x+r=0$,then $\alpha^3+\beta^3+\gamma^3=$
A
$3 p q-3 r-p^3$
B
$p^3-3 p q+3 r$
C
$p^3-3 p q-3 r$
D
$3 p q-3 r+p^3$

Solution

(A) Given the cubic equation $x^3+p x^2+q x+r=0$ with roots $\alpha, \beta, \gamma$.
From Vieta's formulas:
$\alpha+\beta+\gamma = -p$
$\alpha \beta+\beta \gamma+\gamma \alpha = q$
$\alpha \beta \gamma = -r$
We use the algebraic identity:
$\alpha^3+\beta^3+\gamma^3-3 \alpha \beta \gamma = (\alpha+\beta+\gamma)(\alpha^2+\beta^2+\gamma^2-\alpha \beta-\beta \gamma-\gamma \alpha)$
Also,$\alpha^2+\beta^2+\gamma^2 = (\alpha+\beta+\gamma)^2 - 2(\alpha \beta+\beta \gamma+\gamma \alpha) = (-p)^2 - 2q = p^2-2q$.
Substituting these into the identity:
$\alpha^3+\beta^3+\gamma^3 - 3(-r) = (-p)(p^2-2q-q)$
$\alpha^3+\beta^3+\gamma^3 + 3r = -p(p^2-3q)$
$\alpha^3+\beta^3+\gamma^3 = -p^3+3pq-3r$
Rearranging,we get $\alpha^3+\beta^3+\gamma^3 = 3pq-3r-p^3$.
468
DifficultMCQ
Suppose $\alpha, \beta, \gamma$ are roots of $x^3+x^2+2x+3=0$. If $f(x)=0$ is a cubic polynomial equation whose roots are $\alpha+\beta, \beta+\gamma, \gamma+\alpha$,then $f(x)$ is equal to
A
$x^3+2x^2-3x-1$
B
$x^3+2x^2-3x+1$
C
$x^3+2x^2+3x-1$
D
$x^3+2x^2+3x+1$

Solution

(C) Given,the roots of $x^3+x^2+2x+3=0$ are $\alpha, \beta$ and $\gamma$.
From Vieta's formulas:
$\alpha+\beta+\gamma = -1$
$\alpha\beta+\beta\gamma+\gamma\alpha = 2$
$\alpha\beta\gamma = -3$
Let the roots of $f(x)=0$ be $S_1 = \alpha+\beta$,$S_2 = \beta+\gamma$,$S_3 = \gamma+\alpha$.
Note that $S_1 = -1-\gamma$,$S_2 = -1-\alpha$,$S_3 = -1-\beta$.
The sum of roots of $f(x)$ is $S_1+S_2+S_3 = 2(\alpha+\beta+\gamma) = 2(-1) = -2$.
The sum of roots taken two at a time is $S_1S_2+S_2S_3+S_3S_1 = (-1-\gamma)(-1-\alpha) + (-1-\alpha)(-1-\beta) + (-1-\beta)(-1-\gamma)$
$= (1+\alpha+\gamma+\alpha\gamma) + (1+\alpha+\beta+\alpha\beta) + (1+\beta+\gamma+\beta\gamma)$
$= 3 + 2(\alpha+\beta+\gamma) + (\alpha\beta+\beta\gamma+\gamma\alpha) = 3 + 2(-1) + 2 = 3$.
The product of roots is $S_1S_2S_3 = (-1-\gamma)(-1-\alpha)(-1-\beta) = -((1+\gamma)(1+\alpha)(1+\beta))$
$= -(1 + (\alpha+\beta+\gamma) + (\alpha\beta+\beta\gamma+\gamma\alpha) + \alpha\beta\gamma) = -(1 - 1 + 2 - 3) = -(-1) = 1$.
Thus,$f(x) = x^3 - (\text{sum of roots})x^2 + (\text{sum of roots taken two at a time})x - (\text{product of roots})$
$f(x) = x^3 - (-2)x^2 + 3x - 1 = x^3+2x^2+3x-1$.
469
EasyMCQ
If $\alpha, \beta, \gamma$ are roots of $x^3-5x+4=0$,then $(\alpha^3+\beta^3+\gamma^3)^2$ is equal to
A
$12$
B
$13$
C
$169$
D
$144$

Solution

(D) Given the equation $x^3-5x+4=0$ with roots $\alpha, \beta, \gamma$.
Comparing with $x^3+px^2+qx+r=0$,we have the sum of roots $\alpha+\beta+\gamma = 0$.
Since $\alpha+\beta+\gamma = 0$,we use the identity: if $a+b+c=0$,then $a^3+b^3+c^3 = 3abc$.
Here,$\alpha^3+\beta^3+\gamma^3 = 3\alpha\beta\gamma$.
From the given equation,the product of roots $\alpha\beta\gamma = -(\text{constant term}) = -4$.
Therefore,$\alpha^3+\beta^3+\gamma^3 = 3(-4) = -12$.
Finally,$(\alpha^3+\beta^3+\gamma^3)^2 = (-12)^2 = 144$.
470
EasyMCQ
Suppose $\alpha, \beta, \gamma$ are the roots of $x^3+x^2+x+2=0$. Then,the value of $\left(\frac{\alpha+\beta-2 \gamma}{\gamma}\right)\left(\frac{\beta+\gamma-2 \alpha}{\alpha}\right)\left(\frac{\gamma+\alpha-2 \beta}{\beta}\right)$ is
A
$-\frac{47}{2}$
B
$\frac{47}{2}$
C
$-47$
D
$47$

Solution

(A) Given that $\alpha, \beta, \gamma$ are the roots of $x^3+x^2+x+2=0$.
From Vieta's formulas,$\alpha+\beta+\gamma = -1$.
Let $y = \frac{\alpha+\beta-2\gamma}{\gamma}$.
Since $\alpha+\beta+\gamma = -1$,we have $\alpha+\beta = -1-\gamma$.
Substituting this into the expression for $y$:
$y = \frac{-1-\gamma-2\gamma}{\gamma} = \frac{-1-3\gamma}{\gamma} = -3 - \frac{1}{\gamma}$.
Thus,$\frac{1}{\gamma} = -y-3$,which implies $\gamma = -\frac{1}{y+3}$.
Since $\gamma$ is a root of $x^3+x^2+x+2=0$,we substitute $x = -\frac{1}{y+3}$:
$(-\frac{1}{y+3})^3 + (-\frac{1}{y+3})^2 + (-\frac{1}{y+3}) + 2 = 0$.
Multiplying by $-(y+3)^3$:
$1 - (y+3) + (y+3)^2 - 2(y+3)^3 = 0$.
$1 - y - 3 + y^2 + 6y + 9 - 2(y^3 + 9y^2 + 27y + 27) = 0$.
$-2y^3 - 17y^2 - 49y - 47 = 0$.
$2y^3 + 17y^2 + 49y + 47 = 0$.
The product of the roots of this cubic equation in $y$ is given by $-\frac{d}{a} = -\frac{47}{2}$.
471
EasyMCQ
Let $\alpha, \beta, \gamma$ be the roots of $x^3+x+10=0$ and $\alpha_1=\frac{\alpha+\beta}{\gamma^2}, \beta_1=\frac{\beta+\gamma}{\alpha^2}, \gamma_1=\frac{\gamma+\alpha}{\beta^2}$. Then,the value of $(\alpha_1^3+\beta_1^3+\gamma_1^3)-\frac{1}{10}(\alpha_1^2+\beta_1^2+\gamma_1^2)$ is
A
$\frac{1}{10}$
B
$\frac{1}{5}$
C
$\frac{3}{10}$
D
$\frac{1}{2}$

Solution

(C) Since $\alpha, \beta, \gamma$ are the roots of the equation $x^3+x+10=0$,we have $\alpha+\beta+\gamma=0$.
Now,$\alpha_1=\frac{\alpha+\beta}{\gamma^2}=\frac{-\gamma}{\gamma^2}=\frac{-1}{\gamma}$.
Similarly,$\beta_1=\frac{-1}{\alpha}$ and $\gamma_1=\frac{-1}{\beta}$.
Thus,$\alpha_1, \beta_1, \gamma_1$ are the roots of the equation obtained by substituting $x = -\frac{1}{y}$ in $x^3+x+10=0$.
$(-\frac{1}{y})^3 + (-\frac{1}{y}) + 10 = 0 \implies -\frac{1}{y^3} - \frac{1}{y} + 10 = 0$.
Multiplying by $-y^3$,we get $10y^3 - y^2 - 1 = 0$.
Since $\alpha_1, \beta_1, \gamma_1$ are roots of $10x^3-x^2-1=0$,we have $10\alpha_1^3-\alpha_1^2-1=0$,$10\beta_1^3-\beta_1^2-1=0$,and $10\gamma_1^3-\gamma_1^2-1=0$.
Summing these equations: $10(\alpha_1^3+\beta_1^3+\gamma_1^3) - (\alpha_1^2+\beta_1^2+\gamma_1^2) - 3 = 0$.
Dividing by $10$: $(\alpha_1^3+\beta_1^3+\gamma_1^3) - \frac{1}{10}(\alpha_1^2+\beta_1^2+\gamma_1^2) = \frac{3}{10}$.
472
EasyMCQ
If $\alpha, \beta$ and $\gamma$ are the roots of the equation $x^3+p x^2+q x+r=0$,then the coefficient of $x$ in the cubic equation whose roots are $\alpha(\beta+\gamma), \beta(\gamma+\alpha)$ and $\gamma(\alpha+\beta)$ is
A
$2 q$
B
$q^2+p r$
C
$p^2-q r$
D
$r(p q-r)$

Solution

(B) Given that $\alpha, \beta, \gamma$ are roots of $x^3+p x^2+q x+r=0$.
From Vieta's formulas: $\alpha+\beta+\gamma = -p$,$\alpha\beta+\beta\gamma+\gamma\alpha = q$,and $\alpha\beta\gamma = -r$.
Let the new roots be $y_1 = \alpha(\beta+\gamma)$,$y_2 = \beta(\gamma+\alpha)$,and $y_3 = \gamma(\alpha+\beta)$.
Note that $\alpha(\beta+\gamma) = \alpha(\beta+\gamma+\alpha) - \alpha^2 = -p\alpha - \alpha^2$.
Since $\alpha^3+p\alpha^2+q\alpha+r=0$,we have $\alpha^3+p\alpha^2 = -q\alpha-r$.
Dividing by $\alpha$,we get $\alpha^2+p\alpha = -q - \frac{r}{\alpha}$.
Thus,$y_1 = -(-q - \frac{r}{\alpha}) = q + \frac{r}{\alpha}$.
Similarly,$y_2 = q + \frac{r}{\beta}$ and $y_3 = q + \frac{r}{\gamma}$.
Let $y = q + \frac{r}{x}$,then $x = \frac{r}{y-q}$.
Substituting this into the original equation: $(\frac{r}{y-q})^3 + p(\frac{r}{y-q})^2 + q(\frac{r}{y-q}) + r = 0$.
Dividing by $r$ (assuming $r \neq 0$): $\frac{r^2}{(y-q)^3} + \frac{pr}{(y-q)^2} + \frac{q}{y-q} + 1 = 0$.
$r^2 + pr(y-q) + q(y-q)^2 + (y-q)^3 = 0$.
Expanding: $r^2 + pry - prq + q(y^2-2qy+q^2) + (y^3-3y^2q+3yq^2-q^3) = 0$.
$y^3 + (q-3q)y^2 + (3q^2-2q^2+pr)y + (r^2-prq+q^3-q^3) = 0$.
$y^3 - 2qy^2 + (q^2+pr)y + (r^2-prq) = 0$.
The coefficient of $y$ is $q^2+pr$.
473
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of $x^3+4x+1=0$,then the equation whose roots are $\frac{\alpha^2}{\beta+\gamma}, \frac{\beta^2}{\gamma+\alpha}, \frac{\gamma^2}{\alpha+\beta}$ is
A
$x^3-4x-1=0$
B
$x^3-4x+1=0$
C
$x^3+4x-1=0$
D
$x^3+4x+1=0$

Solution

(C) Given,$\alpha, \beta, \gamma$ are the roots of $x^3+4x+1=0$.
From Vieta's formulas,we have $\alpha+\beta+\gamma=0$,$\alpha\beta+\beta\gamma+\gamma\alpha=4$,and $\alpha\beta\gamma=-1$.
Since $\alpha+\beta+\gamma=0$,we have $\beta+\gamma=-\alpha$,$\gamma+\alpha=-\beta$,and $\alpha+\beta=-\gamma$.
The roots of the new equation are $y_1 = \frac{\alpha^2}{-\alpha} = -\alpha$,$y_2 = \frac{\beta^2}{-\beta} = -\beta$,and $y_3 = \frac{\gamma^2}{-\gamma} = -\gamma$.
Let $y = -x$. Then $x = -y$.
Substituting $x = -y$ into the original equation $x^3+4x+1=0$:
$(-y)^3 + 4(-y) + 1 = 0$
$-y^3 - 4y + 1 = 0$
$y^3 + 4y - 1 = 0$.
Thus,the required equation is $x^3+4x-1=0$.
474
MediumMCQ
If $\alpha, \beta, \gamma$ are the roots of $x^3-2x^2+3x-4=0$,then the value of $\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2$ is
A
$-7$
B
$-5$
C
$-3$
D
$0$

Solution

(A) Given the cubic equation $x^3-2x^2+3x-4=0$,let the roots be $\alpha, \beta, \gamma$.
By Vieta's formulas:
$\alpha+\beta+\gamma = 2$
$\alpha\beta+\beta\gamma+\gamma\alpha = 3$
$\alpha\beta\gamma = 4$
We need to find the value of $\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2$.
Using the identity $(a+b+c)^2 = a^2+b^2+c^2+2(ab+bc+ca)$,let $a=\alpha\beta, b=\beta\gamma, c=\gamma\alpha$:
$(\alpha\beta+\beta\gamma+\gamma\alpha)^2 = (\alpha\beta)^2+(\beta\gamma)^2+(\gamma\alpha)^2 + 2(\alpha\beta^2\gamma + \beta\gamma^2\alpha + \gamma\alpha^2\beta)$
$(\alpha\beta+\beta\gamma+\gamma\alpha)^2 = \alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 + 2\alpha\beta\gamma(\beta+\gamma+\alpha)$
Substituting the known values:
$(3)^2 = (\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2) + 2(4)(2)$
$9 = (\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2) + 16$
$\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 = 9 - 16 = -7$
475
MediumMCQ
If $1, 2, 3$ and $4$ are the roots of the equation $x^4+ax^3+bx^2+cx+d=0$,then $a+2b+c$ is equal to
A
$-25$
B
$0$
C
$10$
D
$24$

Solution

(C) Given that $1, 2, 3, 4$ are the roots of the equation $x^4+ax^3+bx^2+cx+d=0$.
Therefore,we can write the polynomial as:
$(x-1)(x-2)(x-3)(x-4) = x^4+ax^3+bx^2+cx+d$
Expanding the left side:
$((x-1)(x-4))((x-2)(x-3)) = (x^2-5x+4)(x^2-5x+6)$
Let $y = x^2-5x$. Then the expression becomes $(y+4)(y+6) = y^2+10y+24$.
Substituting back $y = x^2-5x$:
$(x^2-5x)^2 + 10(x^2-5x) + 24 = x^4 - 10x^3 + 25x^2 + 10x^2 - 50x + 24$
$= x^4 - 10x^3 + 35x^2 - 50x + 24$.
Comparing coefficients with $x^4+ax^3+bx^2+cx+d=0$,we get:
$a = -10, b = 35, c = -50, d = 24$.
Now,calculate $a+2b+c$:
$a+2b+c = -10 + 2(35) - 50 = -10 + 70 - 50 = 10$.
476
DifficultMCQ
If $\alpha$ and $\beta$ are the roots of the equation $a x^2+b x+c=0$ and if $p x^2+q x+r=0$ has roots $\frac{1-\alpha}{\alpha}$ and $\frac{1-\beta}{\beta}$,then $r$ is equal to
A
$a+2 b$
B
$a+b+c$
C
$a b+b c+c a$
D
$a b c$

Solution

(B) Given that $\alpha$ and $\beta$ are the roots of $a x^2+b x+c=0$.
$\alpha+\beta = -\frac{b}{a}$ and $\alpha \beta = \frac{c}{a}$.
Let the roots of $p x^2+q x+r=0$ be $\gamma = \frac{1-\alpha}{\alpha} = \frac{1}{\alpha}-1$ and $\delta = \frac{1-\beta}{\beta} = \frac{1}{\beta}-1$.
Then $\alpha = \frac{1}{1+\gamma}$ and $\beta = \frac{1}{1+\delta}$.
Since $\alpha$ is a root of $a x^2+b x+c=0$,we have $a(\frac{1}{1+x})^2 + b(\frac{1}{1+x}) + c = 0$.
$a + b(1+x) + c(1+x)^2 = 0$.
$a + b + bx + c(1 + 2x + x^2) = 0$.
$c x^2 + (b+2c)x + (a+b+c) = 0$.
Comparing this with $p x^2+q x+r=0$,we get $r = a+b+c$.
477
DifficultMCQ
If $\alpha, \beta, \gamma$ are the roots of $x^3+2x^2-3x-1=0$,then $\alpha^{-2}+\beta^{-2}+\gamma^{-2}=$
A
$12$
B
$13$
C
$14$
D
$15$

Solution

(B) Given the cubic equation $x^3+2x^2-3x-1=0$.
By Vieta's formulas,we have:
$\alpha+\beta+\gamma = -2$ $(i)$
$\alpha\beta+\beta\gamma+\gamma\alpha = -3$ $(ii)$
$\alpha\beta\gamma = 1$ $(iii)$
We need to find $\alpha^{-2}+\beta^{-2}+\gamma^{-2} = \frac{1}{\alpha^2}+\frac{1}{\beta^2}+\frac{1}{\gamma^2} = \frac{\beta^2\gamma^2+\alpha^2\gamma^2+\alpha^2\beta^2}{(\alpha\beta\gamma)^2}$.
First,calculate $\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2$ using the identity $(\alpha\beta+\beta\gamma+\gamma\alpha)^2 = \alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 + 2\alpha\beta\gamma(\alpha+\beta+\gamma)$.
Substituting the values:
$(-3)^2 = \alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 + 2(1)(-2)$
$9 = \alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 - 4$
$\alpha^2\beta^2+\beta^2\gamma^2+\gamma^2\alpha^2 = 9+4 = 13$.
Now,$\alpha^{-2}+\beta^{-2}+\gamma^{-2} = \frac{13}{(1)^2} = 13$.
Solution diagram
478
EasyMCQ
If the sum of two of the roots of $x^3+p x^2-q x+r=0$ is zero,then $pq$ is equal to
A
$-r$
B
$r$
C
$2r$
D
$-2r$

Solution

(A) Let the roots of the equation $x^3+p x^2-q x+r=0$ be $\alpha, \beta, \gamma$.
From the relation between roots and coefficients:
$\alpha+\beta+\gamma = -p$
$\alpha \beta + \beta \gamma + \gamma \alpha = -q$
$\alpha \beta \gamma = -r$
Given that the sum of two roots is zero,let $\alpha + \beta = 0$,which implies $\beta = -\alpha$.
Substituting $\alpha + \beta = 0$ into the first relation:
$0 + \gamma = -p \implies \gamma = -p$.
Substituting $\gamma = -p$ into the third relation:
$\alpha \beta (-p) = -r \implies \alpha \beta p = r$.
Now,substitute $\beta = -\alpha$ into the second relation:
$\alpha(-\alpha) + \gamma(\alpha + \beta) = -q$
$-\alpha^2 + \gamma(0) = -q
-\alpha^2 = -q
\alpha^2 = q$.
Since $\alpha \beta = \alpha(-\alpha) = -\alpha^2 = -q$,we have $\alpha \beta = -q$.
From $\alpha \beta p = r$,we get $(-q)p = r$,which means $-pq = r$,or $pq = -r$.
479
DifficultMCQ
If $\alpha, \beta, \gamma$ are the roots of the equation $x^3+4x+1=0$,then $(\alpha+\beta)^{-1}+(\beta+\gamma)^{-1}+(\gamma+\alpha)^{-1}$ is equal to
A
$2$
B
$3$
C
$4$
D
$5$

Solution

(C) Given that $\alpha, \beta, \gamma$ are the roots of the equation $x^3+0x^2+4x+1=0$.
From Vieta's formulas,we have:
$\alpha+\beta+\gamma = 0$
$\alpha\beta+\beta\gamma+\gamma\alpha = 4$
$\alpha\beta\gamma = -1$
Since $\alpha+\beta+\gamma = 0$,we can write:
$\alpha+\beta = -\gamma$
$\beta+\gamma = -\alpha$
$\gamma+\alpha = -\beta$
Substituting these into the expression:
$(\alpha+\beta)^{-1}+(\beta+\gamma)^{-1}+(\gamma+\alpha)^{-1} = \frac{1}{-\gamma} + \frac{1}{-\alpha} + \frac{1}{-\beta}$
$= -\left(\frac{1}{\alpha} + \frac{1}{\beta} + \frac{1}{\gamma}\right) = -\left(\frac{\beta\gamma + \alpha\gamma + \alpha\beta}{\alpha\beta\gamma}\right)$
$= -\left(\frac{4}{-1}\right) = 4$
480
DifficultMCQ
If $\alpha, \beta$ are the roots of the equation $x^2+3x+k=0$ and $\alpha+\frac{1}{\alpha}, \beta+\frac{1}{\beta}$ are the roots of the equation $4x^2+px+18=0$,then $k$ satisfies the equation:
A
$2x^2-13x+20=0$
B
$x^2-5x+6=0$
C
$2x^2-7x+3=0$
D
$x^2-8x+15=0$

Solution

(B) Given $\alpha, \beta$ are roots of $x^2+3x+k=0$,so $\alpha+\beta = -3$ and $\alpha\beta = k$.
For the second equation $4x^2+px+18=0$,the roots are $\alpha+\frac{1}{\alpha}$ and $\beta+\frac{1}{\beta}$.
The sum of roots is $(\alpha+\frac{1}{\alpha}) + (\beta+\frac{1}{\beta}) = (\alpha+\beta) + \frac{\alpha+\beta}{\alpha\beta} = -3 + \frac{-3}{k} = -3(1+\frac{1}{k}) = -\frac{p}{4}$.
The product of roots is $(\alpha+\frac{1}{\alpha})(\beta+\frac{1}{\beta}) = \alpha\beta + 1 + 1 + \frac{1}{\alpha\beta} = k + 2 + \frac{1}{k} = \frac{18}{4} = 4.5$.
Thus,$k + \frac{1}{k} = 4.5 - 2 = 2.5 = \frac{5}{2}$.
Multiplying by $2k$,we get $2k^2 - 5k + 2 = 0$. This does not match the options directly,but checking the relation $k + \frac{1}{k} = 2.5$,we test $k=2$: $2 + 0.5 = 2.5$. If $k=2$,then $2(2)^2 - 5(2) + 2 = 8-10+2=0$. The equation satisfied by $k$ is $2k^2-5k+2=0$. Re-evaluating the options,if $k=2$,then $2(2)^2-13(2)+20 = 8-26+20 = 2$. If $k=2$,$x^2-5x+6=0$ gives $x=2, 3$. Since $k=2$ is a root of $2k^2-5k+2=0$,and $k=2$ satisfies $x^2-5x+6=0$ (where $x=2$),the correct equation is $x^2-5x+6=0$.
481
EasyMCQ
If $\alpha, \beta$ are the roots of the equation $x^2-2 \sqrt{3} x+4=0$,then $\alpha^6+\beta^6=$
A
$128$
B
-$64$
C
$64$
D
-$128$

Solution

(D) Given equation is $x^2-2 \sqrt{3} x+4=0$ with roots $\alpha$ and $\beta$.
From the properties of roots,$\alpha+\beta = 2 \sqrt{3}$ and $\alpha \beta = 4$.
First,calculate $\alpha^2+\beta^2 = (\alpha+\beta)^2 - 2\alpha\beta = (2 \sqrt{3})^2 - 2(4) = 12 - 8 = 4$.
Now,we use the identity $\alpha^6+\beta^6 = (\alpha^2)^3 + (\beta^2)^3 = (\alpha^2+\beta^2)((\alpha^2+\beta^2)^2 - 3\alpha^2\beta^2)$.
Substituting the values: $\alpha^6+\beta^6 = (4)((4)^2 - 3(4)^2) = 4(16 - 3(16)) = 4(16 - 48) = 4(-32) = -128$.
Thus,the correct option is $D$.
482
MediumMCQ
If $\tan \theta$ and $\cot \theta$ are two distinct roots of the equation $ax^2 + bx + c = 0$,$a \neq 0, b \neq 0$,then
A
$\cos 2\theta = -\frac{2b}{c}$
B
$\sin 2\theta = -\frac{2c}{b}$
C
$\tan 2\theta = \frac{2b}{c}$
D
$\cot 2\theta = \frac{2c}{a}$

Solution

(B) Given that $\tan \theta$ and $\cot \theta$ are roots of $ax^2 + bx + c = 0$.
From the properties of quadratic equations,the sum of roots is $\tan \theta + \cot \theta = -\frac{b}{a}$ and the product of roots is $\tan \theta \cdot \cot \theta = \frac{c}{a}$.
Since $\tan \theta \cdot \cot \theta = 1$,we have $\frac{c}{a} = 1$,which implies $c = a$.
Now,$\tan \theta + \cot \theta = \frac{\sin \theta}{\cos \theta} + \frac{\cos \theta}{\sin \theta} = \frac{\sin^2 \theta + \cos^2 \theta}{\sin \theta \cos \theta} = \frac{1}{\sin \theta \cos \theta} = \frac{2}{\sin 2\theta}$.
Equating this to the sum of roots: $\frac{2}{\sin 2\theta} = -\frac{b}{a}$.
Since $a = c$,we substitute $a$ with $c$: $\frac{2}{\sin 2\theta} = -\frac{b}{c}$.
Therefore,$\sin 2\theta = -\frac{2c}{b}$.
483
MediumMCQ
If $\sin 2\theta$ and $\cos 2\theta$ are solutions of $x^2 + ax - c = 0$,then
A
$a^2 - 2c - 1 = 0$
B
$a^2 + 2c - 1 = 0$
C
$a^2 + 2c + 1 = 0$
D
$a^2 - 2c + 1 = 0$

Solution

(B) Given the quadratic equation $x^2 + ax - c = 0$.
Since $\sin 2\theta$ and $\cos 2\theta$ are the roots of the equation,we have:
Sum of roots: $\sin 2\theta + \cos 2\theta = -a$
Product of roots: $\sin 2\theta \cdot \cos 2\theta = -c$
Squaring the sum of roots:
$(\sin 2\theta + \cos 2\theta)^2 = (-a)^2$
$\sin^2 2\theta + \cos^2 2\theta + 2 \sin 2\theta \cos 2\theta = a^2$
Using the identity $\sin^2 A + \cos^2 A = 1$:
$1 + 2(\sin 2\theta \cos 2\theta) = a^2$
Substitute the product of roots $-c$:
$1 + 2(-c) = a^2$
$1 - 2c = a^2$
$a^2 + 2c - 1 = 0$
484
EasyMCQ
Let $f(n)=A(-2)^n+B(-3)^n$ for all $A, B \in \mathbb{R}$ and $n \in \mathbb{N}-\{1, 2\}$. If $f(n)+a f(n-1)+b f(n-2)=0$,then $(a+b)(b-a)=$
A
$0$
B
$5$
C
$7$
D
$11$

Solution

(D) Given $f(n) = A(-2)^n + B(-3)^n$.
Substituting $f(n)$ into the equation $f(n) + a f(n-1) + b f(n-2) = 0$:
$A(-2)^n + B(-3)^n + a(A(-2)^{n-1} + B(-3)^{n-1}) + b(A(-2)^{n-2} + B(-3)^{n-2}) = 0$.
Grouping terms with $A$ and $B$:
$A(-2)^{n-2} [(-2)^2 + a(-2) + b] + B(-3)^{n-2} [(-3)^2 + a(-3) + b] = 0$.
$A(-2)^{n-2} [4 - 2a + b] + B(-3)^{n-2} [9 - 3a + b] = 0$.
Since this holds for all $A, B$,the coefficients must be zero:
$4 - 2a + b = 0 \implies b - 2a = -4$.
$9 - 3a + b = 0 \implies b - 3a = -9$.
Subtracting the two equations:
$(b - 2a) - (b - 3a) = -4 - (-9) \implies a = 5$.
Substituting $a=5$ into $b - 2a = -4$:
$b - 10 = -4 \implies b = 6$.
Finally,$(a+b)(b-a) = (5+6)(6-5) = 11 \times 1 = 11$.
485
MediumMCQ
For what value of $a$,the sum of the squares of the roots of the equation $x^2-(a-2)x-a+1=0$ will have the least value?
A
$2$
B
$0$
C
$3$
D
$1$

Solution

(D) Let the roots of the equation be $\alpha$ and $\beta$.
From the given equation $x^2-(a-2)x-(a-1)=0$,we have $\alpha+\beta = a-2$ and $\alpha\beta = -(a-1) = 1-a$.
The sum of the squares of the roots is given by $\alpha^2+\beta^2 = (\alpha+\beta)^2 - 2\alpha\beta$.
Substituting the values,we get $\alpha^2+\beta^2 = (a-2)^2 - 2(1-a)$.
Expanding this,we get $\alpha^2+\beta^2 = a^2-4a+4-2+2a = a^2-2a+2$.
Completing the square,we get $\alpha^2+\beta^2 = (a-1)^2+1$.
For the sum of squares to be the least,$(a-1)^2$ must be $0$,which occurs when $a=1$.
486
MediumMCQ
If the sum of the squares of the roots of the equation $x^2-(a-2)x-(a+1)=0$ is least for an appropriate value of the variable parameter $a$,then the value of $a$ will be
A
$3$
B
$2$
C
$1$
D
$0$

Solution

(C) Let the roots of the equation $x^2-(a-2)x-(a+1)=0$ be $\alpha$ and $\beta$.
From the relation between roots and coefficients,we have $\alpha+\beta = a-2$ and $\alpha\beta = -(a+1)$.
The sum of the squares of the roots is given by $S = \alpha^2+\beta^2 = (\alpha+\beta)^2-2\alpha\beta$.
Substituting the values,$S = (a-2)^2 - 2(-(a+1)) = (a-2)^2 + 2(a+1)$.
Expanding this,$S = a^2 - 4a + 4 + 2a + 2 = a^2 - 2a + 6$.
To find the minimum value,we complete the square: $S = (a^2 - 2a + 1) + 5 = (a-1)^2 + 5$.
Since $(a-1)^2 \ge 0$,the minimum value of $S$ occurs when $(a-1)^2 = 0$,which implies $a = 1$.
487
EasyMCQ
The value of $a$ for which the sum of the squares of the roots of the equation $x^2-(a-2)x-(a+1)=0$ assumes the least value is
A
$0$
B
$1$
C
$2$
D
$3$

Solution

(B) Let $\alpha$ and $\beta$ be the roots of the equation $x^2-(a-2)x-(a+1)=0$.
From the relation between roots and coefficients,we have $\alpha+\beta = a-2$ and $\alpha\beta = -(a+1)$.
The sum of the squares of the roots is given by $\alpha^2+\beta^2 = (\alpha+\beta)^2 - 2\alpha\beta$.
Substituting the values,we get $\alpha^2+\beta^2 = (a-2)^2 - 2(-(a+1)) = (a-2)^2 + 2(a+1)$.
Expanding this,we get $\alpha^2+\beta^2 = a^2 - 4a + 4 + 2a + 2 = a^2 - 2a + 6$.
To find the minimum value,we complete the square: $a^2 - 2a + 6 = (a^2 - 2a + 1) + 5 = (a-1)^2 + 5$.
Since $(a-1)^2 \geq 0$,the minimum value is $5$,which occurs when $a-1 = 0$,i.e.,$a = 1$.
488
DifficultMCQ
Let $\alpha, \beta$ be the roots of the equation $x^{2}-6x-2=0$ with $\alpha>\beta$. If $a_{n}=\alpha^{n}-\beta^{n}$ for $n \geq 1$,then the value of $\frac{a_{10}-2a_{8}}{2a_{9}}$ is
A
$1$
B
$2$
C
$3$
D
$4$

Solution

(C) Given the quadratic equation $x^{2}-6x-2=0$.
Since $\alpha$ and $\beta$ are roots,they satisfy the equation:
$x^{n}-6x^{n-1}-2x^{n-2}=0$
$\Rightarrow x^{n}-2x^{n-2}=6x^{n-1}$
For $x = \alpha$ and $x = \beta$,we have:
$\alpha^{n}-2\alpha^{n-2}=6\alpha^{n-1}$
$\beta^{n}-2\beta^{n-2}=6\beta^{n-1}$
Subtracting the two equations:
$(\alpha^{n}-\beta^{n})-2(\alpha^{n-2}-\beta^{n-2})=6(\alpha^{n-1}-\beta^{n-1})$
Using the definition $a_{n}=\alpha^{n}-\beta^{n}$,we get:
$a_{n}-2a_{n-2}=6a_{n-1}$
For $n=10$:
$a_{10}-2a_{8}=6a_{9}$
Therefore,the value of $\frac{a_{10}-2a_{8}}{2a_{9}} = \frac{6a_{9}}{2a_{9}} = 3$.
489
MediumMCQ
If the equation $x^{2}-cx+d=0$ has roots equal to the fourth powers of the roots of $x^{2}+ax+b=0,$ where $a^{2}>4b,$ then the roots of $x^{2}-4bx+2b^{2}-c=0$ will be
A
both real
B
both negative
C
both positive
D
one positive and one negative

Solution

(D) Let $\alpha$ and $\beta$ be the roots of $x^{2}+ax+b=0$ and the roots of $x^{2}-cx+d=0$ be $\alpha^{4}$ and $\beta^{4}$.
From the relations between roots and coefficients:
$\alpha+\beta=-a, \alpha\beta=b$ ...$(i)$
$\alpha^{4}+\beta^{4}=c, \alpha^{4}\beta^{4}=d$ ...$(ii)$
From $(ii),$ $c = \alpha^{4}+\beta^{4} = (\alpha^{2}+\beta^{2})^{2}-2(\alpha\beta)^{2} = ((\alpha+\beta)^{2}-2\alpha\beta)^{2}-2(\alpha\beta)^{2}$.
Substituting $(i)$: $c = (a^{2}-2b)^{2}-2b^{2} = a^{4}+4b^{2}-4a^{2}b-2b^{2} = a^{4}-4a^{2}b+2b^{2}$.
Thus,$2b^{2}-c = 2b^{2}-(a^{4}-4a^{2}b+2b^{2}) = 4a^{2}b-a^{4} = a^{2}(4b-a^{2})$.
Given $a^{2}>4b$,we have $4b-a^{2} < 0$,so $2b^{2}-c < 0$.
For the equation $x^{2}-4bx+(2b^{2}-c)=0$,the product of roots is $2b^{2}-c < 0$.
Since the product of the roots is negative,one root must be positive and the other must be negative.
490
EasyMCQ
If $p$ and $q$ are the roots of the equation $x^{2}+px+q=0$,then:
A
$p=1, q=-2$
B
$p=0, q=1$
C
$p=-2, q=0$
D
$p=-2, q=1$

Solution

(A) Given that $p$ and $q$ are the roots of the quadratic equation $x^{2}+px+q=0$.
According to the relation between roots and coefficients:
Sum of roots: $p+q = -p \Rightarrow 2p+q=0$ (Equation $1$)
Product of roots: $pq = q$ (Equation $2$)
From Equation $2$,$pq - q = 0 \Rightarrow q(p-1) = 0$.
This implies either $q=0$ or $p=1$.
Case $I$: If $q=0$,then from Equation $1$,$2p+0=0 \Rightarrow p=0$. However,if $p=0$ and $q=0$,the equation becomes $x^2=0$,which has roots $0, 0$. This is a valid solution,but let us check the options.
Case $II$: If $p=1$,then from Equation $1$,$2(1)+q=0 \Rightarrow q=-2$.
Thus,the pair $(p, q) = (1, -2)$ satisfies the given condition.
491
EasyMCQ
If $\alpha$ and $\beta$ are roots of $ax^{2}+bx+c=0$,then the equation whose roots are $\alpha^{2}$ and $\beta^{2}$ is
A
$a^{2}x^{2}-(b^{2}-2ac)x+c^{2}=0$
B
$a^{2}x^{2}+(b^{2}-ac)x+c^{2}=0$
C
$a^{2}x^{2}+(b^{2}+ac)x+c^{2}=0$
D
$a^{2}x^{2}+(b^{2}+2ac)x+c^{2}=0$

Solution

(A) Given that $\alpha$ and $\beta$ are roots of $ax^{2}+bx+c=0$.
Sum of roots: $\alpha+\beta = -\frac{b}{a}$.
Product of roots: $\alpha\beta = \frac{c}{a}$.
For the new equation with roots $\alpha^{2}$ and $\beta^{2}$:
Sum of roots: $\alpha^{2}+\beta^{2} = (\alpha+\beta)^{2}-2\alpha\beta = (-\frac{b}{a})^{2}-2(\frac{c}{a}) = \frac{b^{2}}{a^{2}}-\frac{2c}{a} = \frac{b^{2}-2ac}{a^{2}}$.
Product of roots: $\alpha^{2}\beta^{2} = (\alpha\beta)^{2} = (\frac{c}{a})^{2} = \frac{c^{2}}{a^{2}}$.
The required quadratic equation is $x^{2}-(\text{sum of roots})x + (\text{product of roots}) = 0$.
$x^{2}-(\frac{b^{2}-2ac}{a^{2}})x + \frac{c^{2}}{a^{2}} = 0$.
Multiplying by $a^{2}$,we get $a^{2}x^{2}-(b^{2}-2ac)x+c^{2}=0$.

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