If $f(x)=\cos[π]x+\cos[πx]$ where [y] is the greatest integer function of y, then $f(\frac{π}{2})$ is equal to

$\cos 3$ 0 $\cos 4$ none of these

$\cos 4$

$f(\frac{π}{2})=\cos[π].\frac{π}{2}+\cos[π.\frac{π}{2}]=\cos\frac{3π}{2}+\cos 4=\cos 4$