Here are the values of the trigonometric functions at some basic angles. You need not memorize those, but you should be able to figure them out, for example by drawing a suitable picture involving a triangle or the unit circle.
$\cos (0) =$.
$\sin(0) =$.
$\tan(0) =$.
$\cos (\frac{\pi}{2}) =$.
$\sin(\frac{\pi}{2}) =$.