Question

In the given figure, DE || BC and \[AD = \frac{1}{2}BD\]. If BC = 4.5 cm, find DE.

Answer 1

Given: In ∆ABC, DE || BC. `AD = 1/2BD` and BC = 4.5 cm.

To find: DE

In ∆ABC and ∆ADE

\[\angle B = \angle ADE \left( \text{Corresponding angles} \right)\]
\[\angle A = \angle A \left( \text{Common} \right)\]
`∆ABC ~ ∆ADE (A A  "Similarity")`

`(AD)/(AB)=(DE)/(BC)`

`(AD)/(AD+BD)=(DE)/(BC)`

`(1/2BD)/(1/2+BD+BD)=(DE)/(BC)`

`1/3=(DE)/(BC)`

`1/3=(DE)/4.5`

`DE=1.5  cm`