Answer:
x = 15
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 + 20² = 25²
x² + 400 = 625 ( subtract 400 from both sides )
x² = 225 ( take the square root of both sides )
x =
= 15