Chapter 6 - Section 6.3 - Trigonometric Equations Involving Multiple Angles - 6.3 Problem Set - Page 339: 10

$\theta=\{90^o,210^o,330^o\}$

$sin(3\theta)=-1$ $3\theta=sin^{-1}(-1)$ The period of the sine function is $360^o$ $3\theta=270^o\;\;\;\;or\;\;\;\;\;\;3\theta=360^o+270^o\;\;\;\;or\;\;\;\;\;\;3\theta=720^o+270^o\;\;\;\;\;\;\;\;\;\;$ $\theta=90^o\;\;\;\;or\;\;\;\;\;\;\theta=210\;\;\;\;or\;\;\;\;\;\;\theta=330^o\;\;\;\;\;\;\;\;\;\;\;\;\;$ $\theta=\{90^o,210^o,330^o\}$