89.26 Chapter 11. Variation of parameters and other methods. Miscellaneous Exercises at page 177

89.26.1 problem 1
89.26.2 problem 2
89.26.3 problem 3
89.26.4 problem 4
89.26.5 problem 6
89.26.6 problem 7
89.26.7 problem 9
89.26.8 problem 10
89.26.9 problem 11
89.26.10 problem 12
89.26.11 problem 13
89.26.12 problem 14
89.26.13 problem 15
89.26.14 problem 16
89.26.15 problem 17