In Problems 33-40, plot each point given in polar coordinates, and find other polar coordinates $(r, \theta)$ of the point for which:
(a) $r>0, \quad-2 \pi \leq \theta<0$
(b) $r<0, \quad 0 \leq \theta<2 \pi$
(c) $r>0,2 \pi \leq \theta<4 \pi$
$\left(5, \frac{2 \pi}{3}\right)$