1. ## Trig Integral

Having trouble with this problem
$\int COS^2{3x}$

So I used my power reducing formula to get here

$\int \frac{1+cos6X}{2}$

I pull a .5 out front
$\frac12 \int cos6x$

U Sub
$u=6x \ du=6dx$

Put a 1/6 out front
$\frac{1}{12} \int cosUdu \\ = \\ \frac{1}{12}sinx + c$

My book has a different answer, but I think I am right?

2. $\dfrac{1+cos(6x)}{2}=\dfrac{1}{2}(1+cos(6x)) \neq \dfrac{1}{2}(cos(6x))$

3. Ahh yes, thanks for correcting my mistake!