I wish the other tutors would EXPLAIN HOW and WHY they 
get their answers instead of just stating answers.

Here is an explanation as to how and why the other tutor 
just blurted out:

sin(900°) = 0  with no explanation.

Let's find an angle that is coterminal with 900° 
that is less than 360°.  We do a long division by 360°

      2
360)900
    720
    180 

So we see that 900° is two complete revolutions and 
ends up coterminal with 180°,   Below is a picture of
the angle 900°.  The curved arrow shows the rotation
of 2 complete revolutions plus a remainder of 180°:




So we see that 900° has the same trig functions as 180°.

So 

sin(900°) = sin(180°) = 0

and  it you had been asked for the cosine

cos(900°) = cos(900°) = -1.

That is WHY sin(900°) = 0, and cos(900°) = -1.

Edwin