## Precalculus (10th Edition)

$\frac{2}{\pi}$
The general formula for average rate of change from $x$ to $y$ is $\frac{f(y)-f(x)}{y-x}.$ Hence here: $\frac{\sin(\frac{\pi}{2})-\sin(0)}{\frac{\pi}{2}-0}=\frac{1-0}{\frac{\pi}{2}}=\frac{2}{\pi}.$