Find the derivative

\(\displaystyle r=sin^2 3*pi*theta\)

First off, since there are no parentheses in the problem, I don't know if this equals sin(3*pi*theta)^2. I tried that and got a very long answer.

I know the sin will change to cos, but how many of these terms are being operated on by the function of sin?

The book answer was 3pi sin 6pi theta

Thanks.