70.11 Chapter 4. Second order linear equations. Section 4.1 (Definitions and examples). Problems at page 214

70.11.1 problem 1
70.11.2 problem 2
70.11.3 problem 3
70.11.4 problem 4
70.11.5 problem 5
70.11.6 problem 6
70.11.7 problem 7
70.11.8 problem 22
70.11.9 problem 23
70.11.10 problem 24
70.11.11 problem 25
70.11.12 problem 26