78.6 Chapter 7, Nonlinear systems. Problems section 7.11

78.6.1 problem 1
78.6.2 problem 2.a
78.6.3 problem 2.b
78.6.4 problem 2.c
78.6.5 problem 2.d
78.6.6 problem 3.a
78.6.7 problem 3.b
78.6.8 problem 3.c
78.6.9 problem 3.d
78.6.10 problem 4.a
78.6.11 problem 4.b
78.6.12 problem 4.c
78.6.13 problem 4.d
78.6.14 problem 5