Answer:
√39
Explanation:
This triangle is a right triangle, we can use the Pythagoras Theorem.
The hypotenuse or the slanted part of the triangle is c, while the other two are b and a, doesn't matter the order.
In this picture we know what c is and what a (or b, doesn't matter, like I stated before ;w;) is.
a = 5
c = 8
b = x
a^2 + b^2 = c^2
5^2 + x^2 = 8^2
25 + x^2 = 64
x^2 = 64 - 25
x^2 = 39
√x^2 = √39
x = √39