#### Answer

$\frac{\pi}{2}radians$

#### Work Step by Step

In order to convert degree measures to radians, we must multiply the given degree measure by $\frac{\pi}{180}$ and simplify.
$90^{\circ}=90\times(\frac{\pi}{180}radians)=\frac{90\pi}{180}radians=\frac{\pi}{2}radians$