Answer
(a) $\sin{2\pi}=0$
(b) $\cos{2\pi}=1$
(c) $\tan{2\pi}=0$
Work Step by Step
RECALL:
$\sin{s} = y
\\\cos{s} = x
\\\tan{s} = \frac{y}{x}$
The angle $2\pi$ 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,
$\sin{2\pi}=0
\\\cos{2\pi}=1
\\\tan{2\pi}=\frac{0}{1} = 0$