Chapter 7 - Trigonometric Identities and Equations - 7.6 Trigonometric Equations - 7.6 Exercises - Page 721: 65

$\displaystyle \frac{\pi}{3},\ \pi,\ \displaystyle \frac{4\pi}{3}$

If $ 0 \leq x < 2\pi$ then $ 0 \leq 2x < 4\pi$ and $x=\displaystyle \frac{2x}{2}$ so the corresponding values of x are $\displaystyle \frac{\frac{2\pi}{3}}{2}=\frac{\pi}{3},$ $\displaystyle \frac{2\pi}{2}=\pi$ $\displaystyle \frac{\frac{8\pi}{3}}{2}=\frac{4\pi}{3}.$