13.9 Section 2.2.2, Equal roots, reduction of order. Page 147

13.9.1 problem 1
13.9.2 problem 2
13.9.3 problem 3
13.9.4 problem 4
13.9.5 problem 6
13.9.6 problem 7
13.9.7 problem 10
13.9.8 problem 11
13.9.9 problem 12
13.9.10 problem 13
13.9.11 problem 14
13.9.12 problem 15
13.9.13 problem 16
13.9.14 problem 19
13.9.15 problem 20