84.2 Chapter 1. Basic concepts. Supplementary problems

84.2.1 problem 1.6
84.2.2 problem 1.7
84.2.3 problem 1.8
84.2.4 problem 1.9
84.2.5 problem 1.11
84.2.6 problem 1.12
84.2.7 problem 1.13
84.2.8 problem 1.13