I know a) is -1, but I am not sure of b).

Simplify the trigonometric function.
[tex]\begin{gathered} \sin (270^{\circ})=\sin (90^{\circ}+180^{\circ}) \\ =\cos (180^{\circ}\text{)} \\ =-1 \end{gathered}[/tex]The other trigonometric function is cosine and angle is 180 degree.