21 Chapter 5. Applications of Higher Order Equations. Exercises 5.3, page 249

21.1 problem 15
21.2 problem 16
21.3 problem 17
21.4 problem 18
21.5 problem 21 (a)
21.6 problem 21 (b)
21.7 problem 22 (a)
21.8 problem 22 (a)
21.9 problem 24