CPM Homework Help : PC Problem 9-55

What is the average rate of change for the following functions over the given intervals?

$f(x)=\sin(x)$ $\left [\frac{\pi}{2},\pi \right]$
Step (a):
$\frac{\sin(\pi) - \sin\left(\frac{\pi}{2}\right)}{\pi - \frac{\pi}{2}} = ?$

$f(x)=\log x$ $[1, 10]$
Step (b):
$\frac{f(10) - f(1)}{10 - 1} = ?$
Hint (b):
$\log(1)=0$