12.1 problem Ex 1
12.2 problem Ex 2
12.3 problem Ex 3
12.4 problem Ex 4
12.5 problem Ex 5
12.6 problem Ex 6
12.7 problem Ex 7
12.8 problem Ex 8
12.9 problem Ex 10
12.10 problem Ex 11
12.11 problem Ex 12
12.12 problem Ex 13
12.13 problem Ex 14
12.14 problem Ex 15
12.15 problem Ex 16
12.16 problem Ex 17
12.17 problem Ex 18
12.18 problem Ex 19
12.19 problem Ex 20
12.20 problem Ex 21
12.21 problem Ex 22
12.22 problem Ex 23
12.23 problem Ex 24
12.24 problem Ex 25
12.25 problem Ex 26
12.26 problem Ex 27
12.27 problem Ex 28
12.28 problem Ex 29
12.29 problem Ex 30