Chapter 5 - Trigonometric Functions - Section 5.4 Graphs of the Sine and Cosine Functions* - 5.4 Assess Your Understanding - Page 433: 77

$\frac{2}{\pi}$.

1. Given $f(x)=sin(x)$, we have $f(0)=sin(0)=0$ and $f(\frac{\pi}{2})=sin(\frac{\pi}{2})=1$. 2. We have the average rate of change as $R=\frac{f(\frac{\pi}{2})-f(0)}{\frac{\pi}{2}-1}=\frac{1}{\frac{\pi}{2}}=\frac{2}{\pi}$.