Question

proof that cos 2x= 2 ((cos)^2(x))-1

Answer 1

cos 2x = cos (x + x)
by the sum rule,
cos (x + x) = cosx*cosx - sinx*sinx = cos^2(x) - sin^2(x)
since sin^2(x) = 1-cos^2(x)
cos^2(x) - sin^2(x) = cos^2(x) - (1 - cos^2(x))
= cos^2(x) - 1 + cos^2(x))
= 2*cos^2(x) - 1

Answer 2

i got it, thank you