What is the Cartesian form of ( 3 , (16pi)/6 ) ?

$\left(- 3 \frac{\sqrt{3}}{2} , + \frac{3}{2}\right)$
$x = 3 \cos \frac{16 \pi}{6} = 3 \cos \frac{8 \pi}{3} = 3 \cos \frac{2 \pi}{3} = - 3 \cos \frac{\pi}{3} = - 3 \cdot \frac{\sqrt{3}}{2}$
$y = 3 \sin \frac{16 \pi}{6} = 3 \sin \frac{\pi}{3} = \frac{3}{2}$