Number of solutions of \( \sqrt{3} \cos 2\theta + 8 \cos \theta + 3\sqrt{3} = 0, \theta \in [-3\pi, 2\pi] \) is:
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When counting solutions in a large range, draw a simple cosine wave graph. For any value $k$ where $|k|<1$, $\cos \theta = k$ has exactly 2 solutions in every $2\pi$ period.