Evaluate Cos U Assuming That U Is in the Interval $\left(\frac{\pi}{2}, \pi\right)$

Evaluate cos u assuming that u is in the interval $\left(\frac{\pi}{2}, \pi\right)$ And $\sin u=\frac{1}{3}$ .

A) $\frac{\sqrt{8}}{3}$
B) $-\frac{\sqrt{8}}{3}$
C) $\frac{\sqrt{10}}{3}$
D) $-\frac{\sqrt{10}}{3}$