Question

What is the length of the side opposite the 45 degree angle?

Answer 1

Pythagorean theorem. 
a^2 + b^2 = c^2 a^2 = b^2 because this is an isosceles right triangle. c = 10 -- given a^2 + a^2 = 100 2a^2 = 100 a^2 = 50 a = sqrt (50) = 5 sqrt (2) ~ 7.07

Answer 2

Sin 45° = opposite side length/hypotenuse length

Cross Multiply and you get
opposite side length = hypotenuse length x Sin 45°

Now all You need to know is the hypotenuse length. It will help you find the opposite side length.

HOPE THIS WILL HELP.