The Cartesian coordinates of a point are given.
(i) Find polar coordinates $(r, \theta)$ of the point, where $r>0$
and $0 \leqslant \theta<2 \pi$
(ii) Find polar coordinates $(r, \theta)$ of the point, where $r<0$
and $0 \leqslant \theta<2 \pi$
(a) $(-4,4)$
(b) $(3,3 \sqrt{3})$