I could use some help determining the arc length determined by the function:

f(x)=sin xover the interval $\displaystyle [0, \pi]$

I know that I need to use the formula $\displaystyle s = \int_{a}^{b} \sqrt{1 + [f'(x)]^2} dx$

which leads to evaluating: $\displaystyle s = \int_{0}^{\pi} \sqrt{1 + cos^{2}x} dx$,

which looks like it should be easy to do, but I'm just missing it. I've tried Pythagorean Indentity and power reduction formulas to replace $\displaystyle cos^{2}x$ but to no avail. As always, your help would be greatly appreciated.