第13章 13.26

$\sin 3x + \sin\left(x+\dfrac{\pi}{2}\right) = 2\sin\left(2x+\dfrac{\pi}{4}\right)\cos\left(x-\dfrac{\pi}{4}\right) = 2\sin\left(2x+\dfrac{\pi}{4}\right)\sin\left(x+\dfrac{\pi}{4}\right) = \sqrt{3}\sin\left(x+\dfrac{\pi}{4}\right)$

$\sin\left(x+\dfrac{\pi}{4}\right) = 0$ これから $-\dfrac{\pi}{4}+n\pi$

$\sin\left(x+\dfrac{\pi}{4}\right) \neq 0$ のとき

$\sin\left(2x+\dfrac{\pi}{4}\right) = \dfrac{\sqrt{3}}{2}$ これから $\dfrac{\pi}{24}+n\pi$、$\dfrac{5}{24}\pi+n\pi$