Question

Find the value of DE.

Answer 1

DE = 5

Explanation:

The 3 sides of the triangle are congruent , then

DF = EF , that is

`(2)/(5)` a - 15 =
`(1)/(5)` a - 5 ( multiply through by 5 to clear the fractions )

2a - 75 = a - 25 ( subtract a from both sides )

a - 75 = - 25 ( add 75 to both sides )

a = 50

Then

DE = EF =
`(1)/(5)` × 50 - 5 = 10 - 5 = 5