Why is $\cos(x)^2$ written as $\cos^2(x)$?

I'm just wondering why the square of $\cos(x)$ (i.e.: $(\cos(x))*(\cos(x))$) is almost universally written in the form $\cos^2(x)$ rather than $\cos(x)^2$. This seems particularly bizarre when one considers that $\cos^{-1}(x) \ne \cos(x)^{-1}$.