Accedmychevron_right11thchevron_rightmathchevron_rightComplex Numberschevron_rightExercise 1.5

(v)

Given z=103|z|=\dfrac{10}{3} and arg(z)=17π12\arg(z)=-\dfrac{17\pi}{12}.

z=103(cos(17π12)+isin(17π12))z=\frac{10}{3}\left(\cos\left(-\frac{17\pi}{12}\right)+i\sin\left(-\frac{17\pi}{12}\right)\right) 17π12=π5π12-\frac{17\pi}{12}=-\pi-\frac{5\pi}{12} cos(17π12)=cos(π+5π12)=cos5π12=264\cos\left(-\frac{17\pi}{12}\right)=\cos\left(\pi+\frac{5\pi}{12}\right)=-\cos\frac{5\pi}{12}=\frac{\sqrt{2}-\sqrt{6}}{4} sin(17π12)=sin(π+5π12)=sin5π12=6+24\sin\left(-\frac{17\pi}{12}\right)=-\sin\left(\pi+\frac{5\pi}{12}\right)=\sin\frac{5\pi}{12}=\frac{\sqrt{6}+\sqrt{2}}{4} z=5(26)6+5(6+2)6i\boxed{z=\frac{5(\sqrt{2}-\sqrt{6})}{6}+\frac{5(\sqrt{6}+\sqrt{2})}{6}i}