How do you find the integral of int cos^2thetacos2θ?

1 Answer

Use the double angle formula for cosine to reduce the exponent.

Explanation:

cos(2theta) = 2cos^2theta -1cos(2θ)=2cos2θ1

So cos^2theta = 1/2(1+cos(2theta))cos2θ=12(1+cos(2θ))

Hence the integral is

int cos^2theta d(theta)=int 1/2*(1+cos2theta) (d theta)= theta/2+1/4*sin2theta+ccos2θd(θ)=12(1+cos2θ)(dθ)=θ2+14sin2θ+c