삼각방정식 실근 합

$( 1 - \sin ^{2} 3 x ) - \sin 3 x + 1 = 0$ $\sin ^{2} 3 x + \sin 3 x - 2 = 0$ $( \sin 3 x + 2 ) ( \sin 3 x - 1 ) = 0$ $\sin 3 x = 1$, $\displaystyle 3 x = \frac{\pi}{2}$, $\displaystyle \frac{5}{2} \pi$, $\displaystyle \frac{9}{2} \pi$ $\displaystyle x = \frac{1}{6} \pi$, $\displaystyle \frac{5}{6} \pi$, $\displaystyle \frac{9}{6} \pi$이므로 그 합은 $\displaystyle \frac{5}{2} \pi$