Show that Cos 2x = 1 - 2 sin^2 x

Presume you know the formula for Cos(a+b) which is CosA.CosB - SinA.SinB

Cos(x+x) = cos(x)*cos(x) - sin(x)*sin(x)
Cos 2x = cos^2 (x) - sin^2 (x)
= 1- sin^2 (x) - sin^2 (x), since sin^2x + cos^2 x = 1
= 1 - 2*sin^2 (x)