Answer
$\frac{7\pi}{4}$
Work Step by Step
Using trigonometric identities, we have
$cos(\frac{\theta}{3}-\frac{\pi}{4})=\frac{1}{2} \longrightarrow \frac{\theta}{3}-\frac{\pi}{4}=\frac{\pi}{3} \longrightarrow \theta=\frac{7\pi}{4}$
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