Area of a region enclosed by polar equation

I have this problem that reads "Find the area enclosed by $\displaystyle r^2$ = $\displaystyle 4cos(\theta)

$."

so, what I ended up with

2$\displaystyle

\int_a^b$ $\displaystyle cos(\theta)$ $\displaystyle d\theta$

I may have messed up in finding the correct integral, but I think the problem is that I don't know what to choose for $\displaystyle a$ or $\displaystyle b$. Can anyone help explain how I would go about choosing proper values for $\displaystyle a$ and $\displaystyle b$?

P.S. I seem to be having trouble with the LaTex, is anyone else having trouble?