78.7 Chapter 2. First order equations. Section 11 (Reduction of order). Problems at page 87

78.7.1 problem 1 (a)
78.7.2 problem 1 (b)
78.7.3 problem 1 (c)
78.7.4 problem 1 (d)
78.7.5 problem 1 (e)
78.7.6 problem 1 (f)
78.7.7 problem 1 (g)
78.7.8 problem 2 (a)
78.7.9 problem 2 (b)
78.7.10 problem 2 (c)
78.7.11 problem 3 (a)
78.7.12 problem 3 (b)