Pythagorean Style Solving

When solving the types of questions asking you what the cos(x) if the sin(x) = 7/8 (or some similar problem. Set an equation equal to cos^2(t) =1 - sin^2 (x). Substitute the value: 1- (7/8)^2 and simplify.

64/64 - 49/64
15/64=cos^2(x)
square root of 15/64= root 15/8