Answer:
4

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.
let x represent the third side, then
x² + 4² = 8²
x² + 16 = 64 ( subtract 16 from both sides )
x² = 48 ( take square root of both sides )
x =
=
=
×
= 4
