How do you find the integral of int [cos^3 (2x)] dx [cos3(2x)]dx?

1 Answer
Sep 21, 2015

1/2sin 2x-1/6sin^3 2x+C12sin2x16sin32x+C

Explanation:

I=int cos^3 2xdx = int cos 2x cos^2 2x dxI=cos32xdx=cos2xcos22xdx
I=int cos 2x (1-sin^2 2x)dxI=cos2x(1sin22x)dx

sin 2x=t => 2cos 2xdx = dt => cos 2xdx = dt/2sin2x=t2cos2xdx=dtcos2xdx=dt2

I=int(1-t^2)dt/2=1/2(t-t^3/3)+CI=(1t2)dt2=12(tt33)+C

I=1/2sin 2x-1/6sin^3 2x+CI=12sin2x16sin32x+C