# How do you prove cos2A = 2cos^2 A - 1?

##### 1 Answer
Apr 20, 2015

Probably it is not very much as a "proof" but...
if A=30°
2A=60°
so:
cos(60°)=1/2
2cos^2(30°)-1=2(sqrt(3)/2)^2-1=3/2-1=1/2