Find y' given the following function:

$\displaystyle y=\ln{(5x^2+y^2)}$

So far, I have:

$\displaystyle y'=\frac{10x+2y*y'}{5x^2+y^2} $

Having trouble combining the y's.

Another one I am stuck on is:

$\displaystyle y=(\ln{(x)})^{cos(15x)} $

I am not positive if it is okay to bring the cos(15x) into the front of the ln in this case?

Thanks for any help!