複素数を極形式で表す（B）

(1) $r=2$，$\cos\theta=\dfrac{\sqrt{3}}{2}$，$\sin\theta=-\dfrac{1}{2}$ より $\theta=\dfrac{11}{6}\pi$．$2\left(\cos\dfrac{11}{6}\pi+i\sin\dfrac{11}{6}\pi\right)$ (2) $r=2\sqrt{2}$，$\cos\theta=\sin\theta=-\dfrac{1}{\sqrt{2}}$ より $\theta=\dfrac{5}{4}\pi$．$2\sqrt{2}\left(\cos\dfrac{5}{4}\pi+i\sin\dfrac{5}{4}\pi\right)$ (3) $r=4$，$\theta=\dfrac{\pi}{2}$．$4\left(\cos\dfrac{\pi}{2}+i\sin\dfrac{\pi}{2}\right)$ (4) $r=\sqrt{3+9}=2\sqrt{3}$，$\cos\theta=\dfrac{-\sqrt{3}}{2\sqrt{3}}=-\dfrac{1}{2}$，$\sin\theta=\dfrac{3}{2\sqrt{3}}=\dfrac{\sqrt{3}}{2}$ より $\theta=\dfrac{2}{3}\pi$．$2\sqrt{3}\left(\cos\dfrac{2}{3}\pi+i\sin\dfrac{2}{3}\pi\right)$