How do you evaluate #sin(0)#?
Use the unit circle to evaluate it to be 0.
(This one's from Wikipedia, but any version of it will be more or less the same.)
On the unit circle, the x-coordinate at each position is the cosine of the given angle, and the y-coordinate is the sine.
If you're not at the point where you need to use the unit circle yet, it will probably be more useful to just memorize that