# What is an angle between 0 and 2pi that is coterminal with -9pi/4?

$\frac{7 \pi}{4}$
Keep adding a full rotation until you get a coterminal angle in your interval $\left[0 , 2 \pi\right]$
$\frac{- 9 \pi}{4} + \frac{8 \pi}{4} = \frac{- \pi}{4}$ (Close! Not there yet, though...)
$\frac{- \pi}{4} + \frac{8 \pi}{4} = \frac{7 \pi}{4}$ Between $\left[0 , 2 \pi\right]$! Done!