Consider a<span> right triangle with </span><span>hypotenuse of 1. sin x means to divide the side in front of the angle by </span>hypotenuse<span> cos x means to divide the side beside the angle by hypotenuse we know that a^2+b^2=c^2 now divide two sides by c^2 c is 1 also a/c means sinx and b/c is cos x so sin^2(x)+cos^2(x)=1