# Help with an integral

1. Feb 22, 2010

### KaiserBrandon

1. The problem statement, all variables and given/known data

I can't seem to figure out how to solve this integral:

$$\int$$cos2(2$$\Theta$$)d$$\Theta$$

2. Relevant equations

none

3. The attempt at a solution

I tried doing integration by parts by first letting v=d$$\Theta$$ and dV=$$\Theta$$, and U=cos2(2$$\Theta$$) and dU=-4$$\Theta$$cos(2$$\Theta$$)sin(2$$\Theta$$)d$$\Theta$$, and then putting it into the form $$\int$$UdV=UV-$$\int$$VdU, but that didn't really take me anywhere. Is there another way I should try to solve this integral? This is my fourth university calc class, and the full question is double integrals with polar coordinates, so I probably learned how to solve these types of integrals somewhere down the road, I just can't seem to remember. Thanks in advance
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 22, 2010

### Staff: Mentor

Hint: cos2(t) = (cos(2t) + 1)/2