Answer
$sin(-\frac{7\pi}{3})=-\frac{\sqrt 3}{2}$
$cos(-\frac{7\pi}{3})=\frac{1}{2}$
$tan(-\frac{7\pi}{3})=-\sqrt 3$
Work Step by Step
Let $θ'$ be the reference angle. We must have that $0\leqθ'\lt2\pi$
$θ'=θ+n·2\pi$, where $n$ is an integer.
$θ'=-\frac{7\pi}{3}+2·2\pi=\frac{5\pi}{3}$
$sin(-\frac{7\pi}{3})=sin\frac{5\pi}{3}=-\frac{\sqrt 3}{2}$
$cos(-\frac{7\pi}{3})=cos\frac{5\pi}{3}=\frac{1}{2}$
$tan(-\frac{7\pi}{3})=tan\frac{5\pi}{3}=-\sqrt 3$
