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
$$\begin{array}\text{ a.} \quad r>0, \quad 2 \pi<\theta<4 \pi \\ \text{b.}\quad r<0, \quad 0<\theta<2 \pi \\
\text{c.}\quad r>0, \quad -2 \pi<\theta<0\end{array}$$
$$\left(8, \frac{\pi}{6}\right)$$