Answer
(b) and (d)
Work Step by Step
Please note that if $n$ is any integer, the point $(r, \theta )$ can be represented as$$(r, \theta ) = (r, \theta +2n\pi ) \\ \text{or} \\ (r, \theta )= (-r, \theta +\pi + 2n\pi ).$$So we have$$(2, -\frac{3\pi }{4})= (2, -\frac{3\pi }{4}+2(1)\pi)=(2, \frac{5\pi }{4}) \\ (2, -\frac{3\pi }{4})= (-2, -\frac{3\pi }{4}+\pi +2(-1)\pi )=(-2, -\frac{7\pi }{4}).$$
