Question Number 115248 by aye48 last updated on 24/Sep/20

Express cos 4x interm of cos x.

Answered by Olaf last updated on 24/Sep/20

cos4x = 2cos^2 2x−1  cos4x = 2(2cos^2 x−1)^2 −1  cos4x = 2(4cos^4 x−4cos^2 x+1)−1  cos4x = 8cos^4 x−8cos^2 x+1