Question

Find the value of DE.

Answer 1

Answer:

DE = 5

Step-by-step explanation:

The 3 sides of the triangle are congruent , then

DF = EF , that is

$\frac{2}{5}$ a - 15 = $\frac{1}{5}$ 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 = $\frac{1}{5}$ × 50 - 5 = 10 - 5 = 5