Chapter 3 - Radian Measure and the Unit Circle - Section 3.3 The Unit Circle and Circular Functions - 3.3 Exercises - Page 117: 5

(a) $\sin{(-\pi)}=0$ (b) $\cos{(-\pi)}=-1$ (c) $\tan{(-\pi)}=0$

RECALL: $\sin{s} = y \\\cos{s} = x \\\tan{s} = \frac{y}{x}$ The angle $-\pi$ ($\pi$ degrees clockwise) will intersect the unit circle at the point $(-1, 0)$ (refer to Figure 15 on page 113). The point $(-1, 0)$ has: $x=-1 \\y=0$ Thus, $\sin{(-\pi)}=0 \\\cos{(-\pi)}=-1 \\\tan{(-\pi)}=\frac{0}{-1} = 0$