Use a polar coordinate system like the one shown for Exercises 1–10 to plot each point with the given polar coordinates. Then find another representation (r, $\theta$) of this point
in which.
$$\text { a. } r>0, \quad 2 \pi<\theta<4 \pi$$
$$\text { b. } r<0, \quad 0<\theta<2 \pi$$
$$\text { c. } r>0, \quad-2 \pi<\theta<0$$
$$
\left(4, \frac{\pi}{2}\right)
$$