Rectangular to polar coordinates

Hi,
I was wondering if someone could please tell me if my first step is right for converting (x^2 + y^2)^2 + 2*(x^2 + y^2) - 4*x^2 to polar coordinates.

(r^2)^2 + 2r^2 - 4*(r cos^2(t))

Thanks Brendan

The last r should be squared as well: (r^2)^2 + 2r^2 - 4*(r^2 cos^2(t))

Thanks Jemidiah