Question

cos^2(x)=1+cos(2x) / 2

HELP PLEASE THANKS

Answer 1

in your previous post we just proved:

cos (2x) = cos^2 x - sin^2 x
but sin^2 x = 1 - cos^2 x
so
cos (2x) = cos^2 x - (1 - cos^2 x)
= 2 cos^2 x - 1
2cos^2 x = 1 + cos(2x)
cos^2 x = (1 + cos(2x) )/2