Recent content by mathismyworld

Homework Statement Derive sin^2 + cos^2 = 1 Homework Equations Use cos 0 =1, cos (x+y) = cos x cos y - sin x sin y Earlier someone posted this same question, but I still don't understand it so please help

sorry but can anyone please explain it to me again? i don't understand why you have to choose a value for y and not x and i don't see how even/odd functions will be used