# What is the Cartesian form of ( -9, (-7pi)/3 ) ?

$\left(- \frac{9}{2} , 9 \frac{\sqrt{3}}{2}\right)$
r =$- 9$ and $\theta = - 7 \frac{\pi}{3}$.
$x = r \cos \theta = - 9 \cos \left(- 7 \frac{\pi}{3}\right) = - 9 \cos \left(7 \frac{\pi}{3}\right) = - 9 \cos \left(2 \pi + \frac{\pi}{3}\right) = - 9 \cos \left(\frac{\pi}{3}\right) = - \frac{9}{2}$.
Similarly, y = $9 \frac{\sqrt{3}}{2}$