Answer
$a.$
$(1,\displaystyle \frac{7\pi}{4}), \quad (1,\frac{15\pi}{4})\quad (-1,\frac{11\pi}{4}) \quad$all represent the same point $A$.
$b.$
$(-3,\displaystyle \frac{\pi}{6}), \quad(-3,\frac{13\pi}{6}), \quad(+3,\frac{7\pi}{6}), \quad$all represent the same point $B.$
$c.$
$(1,-1), \quad (1,-1+2\pi),\quad (-1,-1+\pi),\quad$ all represent the same point $C$.
Work Step by Step
$2(r,\theta\pm 2k\pi),\ k\in \mathbb{Z}$ and $(r,\theta)$ represent the same point
$(-r,\theta\pm 2k\pi),\ k\in \mathbb{Z}$ represent the point symmetric to $(r,\theta)$, over the pole (origin).
$(r,\theta\pm(2k+1)\pi),\ k\in \mathbb{Z}$ represent the point symmetric to $(r,\theta)$, over the pole (origin).
$(-r,\theta\pm(2k+1)\pi),\ k\in \mathbb{Z}$ and $(r,\theta)$ represent the same point.
Leaving the same r, adding an even multiple of $\pi$ to $\theta$ yields the same point.
Changing the sign of r, adding an odd multiple of $\pi$ to $\theta$ yields the same point.
$a.$
$(1,\displaystyle \frac{7\pi}{4}), \quad (1,\frac{15\pi}{4})\quad (-1,\frac{11\pi}{4}) \quad$all represent the same point $A$.
$b.$
$(-3,\displaystyle \frac{\pi}{6}), \quad(-3,\frac{13\pi}{6}), \quad(+3,\frac{7\pi}{6}), \quad$all represent the same point $B.$
$c.$
$(1,-1), \quad (1,-1+2\pi),\quad (-1,-1+\pi),\quad$ all represent the same point $C$.
