Chapter 7 - Trigonometric Identities and Equations - 7.6 Trigonometric Equations - 7.6 Exercises - Page 721: 67

$60^{o}$ , $210^{o},\ 240^{o},\ 310^{o}$

If $0 \leq \theta < 360^{o}$ then $0 \leq 3\theta < 1080^{o},$ and $\theta=(3\theta)\div 3$ so the corresponding values of $\theta$ are $180^{o}\div 3=60^{o},$ $630^{o}\div 3=210^{o},$ $720^{o}\div 3=240^{o},$ $930^{o}\div 3=310^{o}$.