Answer
$a.\displaystyle \qquad\frac{1}{2} \\$
$b. \qquad 2 \\$
$c. \displaystyle \qquad -\frac{\sqrt{3}}{2}$
Work Step by Step
$ a.\displaystyle \qquad \cos(-\frac{\pi}{3})=\qquad$... even/odd properties,
$=\displaystyle \cos(\frac{\pi}{3})=\qquad$...table p.410 ...
$=\displaystyle \frac{1}{2}$
$ b.\displaystyle \qquad \sec(-\frac{\pi}{3})=\qquad$... even/odd properties,
$=\displaystyle \sec(\frac{\pi}{3})=\qquad$...table p.410 ...
$=2$
$ c. \displaystyle \qquad \sin(-\frac{\pi}{3})=\qquad$... even/odd properties,
$=-\displaystyle \sin(\frac{\pi}{3})=\qquad$...table p.410 ...
$=-\displaystyle \frac{\sqrt{3}}{2}$