We will have the following:
[tex](5(\cos (\frac{\pi}{2})+i\sin (\frac{\pi}{2})))\cdot(2(\cos (\frac{5\pi}{5})+i\sin (\frac{5\pi}{6})))=10(\cos (-\frac{2\pi}{3})+i\sin (-\frac{2\pi}{3}))[/tex][tex]=10(\cos (\frac{4\pi}{3})+i\sin (\frac{4\pi}{3}))[/tex][We exploit the fact that trigonometric funtions are cyclical to determine the answer.
[Option B]
