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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  $\frac{AD}{DB}\ =\ \frac{3}{4}$ and $AC\ =\ 15\ cm$, 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 $DE\ ||\ BC$.


$\frac{AD}{DB}\ =\ \frac{3}{4}$ and $AC\ =\ 15\ cm$.


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,

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

$\frac{3}{4} + 1 =\frac{AE+EC}{EC}$    ($\frac{AD}{DB}\ =\ \frac{3}{4}$)

$\frac{3+4}{4} =\frac{AC}{EC}$    ($AE+EC=AC$)

$\frac{7}{4} =\frac{15}{EC}$

$EC= \frac{15\times4}{7}$

$EC=\frac{60}{7} cm$

$AE=AC-EC$

$AE=15-\frac{60}{7} cm$

$AE=\frac{15\times7-60}{7}$

$AE=\frac{105-60}{7}$

$AE=\frac{45}{7} cm$

The measure of $AC$ is $\frac{45}{7} cm$.

Updated on: 10-Oct-2022

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