trigonometry

The Pythagorean theorem:
c^2 = x^2 + y^2 where c is the hypotenuse of a right triangle and x, y are the sides.

c = x(2^1/2)
c^2 = x^2(2^1/2)^2
c^2 = x^2(2)
c^2 = x^2 + x^2

let x = y

c^2 = x^2 + y^2