81.2 Chapter 3. Exact differential equations. Page 42.

81.2.1 problem 3-1
81.2.2 problem 3-2
81.2.3 problem 3-3
81.2.4 problem 3-4
81.2.5 problem 3-6
81.2.6 problem 3-7
81.2.7 problem 3-8
81.2.8 problem 3-9
81.2.9 problem 3-10
81.2.10 problem 3-11