4 Section 3.12, Systems of differential equations. The nonhomogeneous equation. variation of parameters. Page 366

4.1 problem Example 1, page 361
4.2 problem Example 2, page 364
4.3 problem 1
4.4 problem 2
4.5 problem 3
4.6 problem 4
4.7 problem 5
4.8 problem 6
4.9 problem 10
4.10 problem 11
4.11 problem 12
4.12 problem 13
4.13 problem 14
4.14 problem 16
4.15 problem 17
4.16 problem 18