Chapter 18 "Second-order Differential Equations"
Textbook sections that will be covered are 18.1 to 18.3. The following are recommended exercises:
18.1: 1, 3, 5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 27, 33
18.2: 1, 3, 5, 7, 9, 13, 15, 17, 19, 21, 23, 25
18.3: 1, 3, 5, 9, 11, 13, 15
The following links should give you a introduction to second-order differential equations and show you how to work with them:
http://www.sosmath.com/diffeq/diffeq.html
http://math.furman.edu/~dcs/book/c8pdf/sec84.pdf