Question 180080
Always, always draw the angle in the quadrant it belongs in.
The angle is a rotating vector with the sine or cosine wave
projected along the x-axis.
  It helps if you can draw or at least picture the sine wave
as the vector rotates around the circle through the
quadrants. You really need this complete picture every time
and it's worth the effort
sin(210) = sin (180 + 30) = -(1/2)
It's in the 3rd quadrant where the sin is negative
cos(135) = cos(90 + 45) = -(1/{{{sqrt(2)}}})
It's in the 2nd quadrant where the cos is negative