In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$. Prove that $BD = \frac{BC \times AB}{AB + AC}$ and $DC = \frac{BC \times AC}{AB + AC}$.

Vedclass pdf generator app on play store
Vedclass iOS app on app store
(N/A) In $\Delta ABC$,the bisector of $\angle A$ intersects $\overline{BC}$ at $D$.
By the Angle Bisector Theorem,we have:
$\frac{AB}{AC} = \frac{BD}{DC}$
To find $BD$:
$\frac{AB}{AC} = \frac{BD}{DC}$
Using the property of Componendo,$\frac{AB + AC}{AC} = \frac{BD + DC}{DC} = \frac{BC}{DC}$
This does not directly give $BD$. Let's use $\frac{AB}{AC} = \frac{BD}{DC} \implies \frac{AB}{AB + AC} = \frac{BD}{BD + DC} = \frac{BD}{BC}$
$\therefore BD = \frac{BC \times AB}{AB + AC}$
To find $DC$:
$\frac{AB}{AC} = \frac{BD}{DC} \implies \frac{AC}{AB} = \frac{DC}{BD}$
Using Componendo,$\frac{AC + AB}{AB} = \frac{DC + BD}{BD} = \frac{BC}{BD}$
$\implies \frac{AC}{AC + AB} = \frac{DC}{BC}$
$\therefore DC = \frac{BC \times AC}{AB + AC}$

Explore More

Similar Questions

In $\Delta ABC$,$\overline{AD}$ is a median. If $AB = 8$,$AC = 15$ and $AD = 8.5$,find $BC$.

In $\Delta ABC$,$m \angle B = 90^{\circ}$ and $\overline{BM}$ is an altitude to the hypotenuse $\overline{AC}$. If $AM = 4$ and $CM = 5$,find $AB$,$BC$,and $BM$.

$\square ABCD$ 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 $\frac{AO}{AC}$.

Difficult
View Solution

In the figure,if $DE \parallel BC,$ find the ratio of $\operatorname{ar}(ADE)$ and $\operatorname{ar}(DECB).$

Difficult
View Solution

In $\Delta ABC$,$m\angle B = 90^{\circ}$ and $\overline{BM}$ is a median. If $AB = 15$ and $BM = 12.5$,find $BC$.

Vedclass Products

For Students

Vedclass Test Series

Mock tests in real JEE/NEET style with performance analysis. 5-day free trial.

Start Free Trial
For Teachers

Exam Paper Generator

Generate Set A/B/C/D exam papers from 7.5L+ questions in 2 minutes. 3 chapters free.

Try Free
For Institutes

Online Exam Module

Live online exams with unlimited students, 360° analytics & white-label branding.

See Demo