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In a $Δ\ ABC$, $D$ and $E$ are points on the sides $AB$ and $AC$ respectively such that $DE\ ||\ BC$.
If  $\frac{AD}{DB}\ =\ \frac{2}{3}$ and  $AC\ =\ 18\ cm$, find $AE$.

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Given:


In a $Δ\ ABC$, $D$ and $E$ are points on the sides $AB$ and $AC$ respectively such that $DE\ ||\ BC$.


$\frac{AD}{DB}\ =\ \frac{2}{3}$ and $AC\ =\ 18\ cm$.


To do:


We have to find the measure of $AE$.

Solution:


$DE\ ||\ BC$ (given)

Therefore,

By Basic proportionality theorem,

$\frac{AD}{DB}\ =\ \frac{AE}{EC}$


Adding $1$ on both sides,

$\frac{AD}{DB} + 1 = \frac{AE}{EC} + 1$

$\frac{2}{3} + 1 =\frac{AE+EC}{EC}$    ($\frac{AD}{DB}\ =\ \frac{2}{3}$)

$\frac{2+3}{3} =\frac{AC}{EC}$    ($AE+EC=AC$)

$\frac{5}{3} =\frac{18}{EC}$

$EC= \frac{18\times3}{5}$

$EC=\frac{54}{5} cm$

$AE=AC-EC$

$AE=18-\frac{54}{5} cm$

$AE=\frac{18\times5-54}{5}$

$AE=\frac{90-54}{5}$

$AE=\frac{36}{5} cm$

$AE=7.2 cm$

The measure of $AC$ is $7.2 cm$. 

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Updated on: 10-Oct-2022

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