Chapter 3 - Radian Measure and the Unit Circle - Section 3.3 The Unit Circle and Circular Functions - 3.3 Exercises - Page 123: 15

(a) 0 (b) -1 (c) 0

$-\pi$ is coterminal with $-\pi+2\pi=\pi$. Coterminal angles intersects the unit circle at the same point. An angle of $\pi$ radians intersects the unit circle at the point $(-1,0)$. So is the angle $-\pi$. (a) $\sin s= y= 0$ (b) $\cos s=x=-1$ (c) $\tan s=\frac{y}{x}=\frac{0}{-1}=0$