\textbf{108.} The sum of all solutions of the equation $\sin 4x = \sin^2 x - \cos^2 x$, in the interval $[0, \pi]$, equals which of the following?
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(4) $\dfrac{11\pi}{2}$ \hfill (3) $\dfrac{5\pi}{2}$ \hfill (2) $\dfrac{9\pi}{4}$ \hfill (1) $\dfrac{7\pi}{4}$
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