20.18 Chapter 9, First order linear systems. Section 9.6 (Variation of parameters for linear systems), page 624

20.18.1 problem 1
20.18.2 problem 2
20.18.3 problem 3
20.18.4 problem 4
20.18.5 problem 5
20.18.6 problem 6
20.18.7 problem 7
20.18.8 problem 8
20.18.9 problem 9
20.18.10 problem 11