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

9.1 problem 1
9.2 problem 2
9.3 problem 3
9.4 problem 4
9.5 problem 6
9.6 problem 7
9.7 problem 10
9.8 problem 11
9.9 problem 12
9.10 problem 13
9.11 problem 14
9.12 problem 15
9.13 problem 16
9.14 problem 19
9.15 problem 20