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

76.11.1 problem 1
76.11.2 problem 2
76.11.3 problem 3
76.11.4 problem 4
76.11.5 problem 5
76.11.6 problem 6
76.11.7 problem 7
76.11.8 problem 22
76.11.9 problem 23
76.11.10 problem 24
76.11.11 problem 25
76.11.12 problem 26