Answer
$\frac{7\pi}{4}$
Work Step by Step
$cos(\frac{\theta}{3}-\frac{\pi}{4})=\frac{1}{2}$,
$\frac{\theta}{3}-\frac{\pi}{4}=2k\pi+\frac{\pi}{3}$ or $2k\pi-\frac{\pi}{3}$
$\theta=6k\pi+\frac{7\pi}{4}$ or $6k\pi-\frac{\pi}{4}$ (k is an integer),
$\theta=\frac{7\pi}{4}$ in $[0,2\pi)$.
