\textbf{109-} What is the general solution of the trigonometric equation $\dfrac{\sin 3x}{\sin x}=2\cos^2 x$?
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(1) $\dfrac{k\pi}{2}$ \hfill (2) $\dfrac{k\pi}{2}+\dfrac{\pi}{4}$ \hfill (3) $k\pi-\dfrac{\pi}{4}$ \hfill (4) $k\pi+\dfrac{\pi}{4}$
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