## Precalculus (6th Edition) Blitzer

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$$(4, 120^{\circ })= (4, 120^{\circ }+2(-1)180^{\circ })=(4, -240^{\circ }) \\ (4, 120^{\circ })= (4, 120^{\circ } +2(1)180^{\circ })=(4, 480^{\circ }) \\ (4, 120^{\circ })= (-4, 120^{\circ }+180^{\circ }+2(0)180^{\circ })=(-4, 300^{\circ})$$