84.30 Chapter 18. Linear differential equations with variable coefficients. Supplementary problems

84.30.1 problem 18.11
84.30.2 problem 18.12
84.30.3 problem 18.13
84.30.4 problem 18.14
84.30.5 problem 18.15
84.30.6 problem 18.16
84.30.7 problem 18.17
84.30.8 problem 18.18
84.30.9 problem 18.19