x = 37.5 (or) 
Solution:
Given 
AC = 50, DE = 30, EC = 25, BE = x, BC = 25 + x
To find the value of x:
Property of similar triangles:
If two triangles are similar then the corresponding angles are congruent and the corresponding sides are in proportion.


Do cross multiplication, we get


Subtract 30x from both sides of the equation.

Divide by 20 on both sides of the equation, we get
x = 37.5 (or) 
Hence the value of x is 37.5 or
.
I know Iscoscles and acute only
The two labeled angles are alternate interior angles, and as such, they are the same.
From this result you can build the equation

and solve it for x: subtract 13x from both sides to get

and add 2 to both sides to get

Check: if we plug the value we found we have

So the angles are actually the same, as requested.
Answer:
x = 5
Step-by-step explanation:
Using Pythagoras' identity in the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
x² + 12² = 13², so
x² + 144 = 169 ( subtract 144 from both sides )
x² = 25 ( take the square root of both sides )
x =
= 5