Good video on differentials and linear approximations:
https://www.youtube.com/watch?v=CMeJYSvXKxc
The link below has some more worked out examples (scroll down and you'll find them)
http://www.cliffsnotes.com/math/calculus/calculus/applications-of-the-derivative/differentials
HW: Complete the 4 question 3.7 practice quiz (answers are posted on the AP Calc page) and complete the 1 - 2 on the WS Linear Approximation Homework.