4.1 problem Recognizable Exact Differential equations. Integrating factors. Example 10.51, page 90
  4.2 problem Recognizable Exact Differential equations. Integrating factors. Example 10.52, page 90
  4.3 problem Recognizable Exact Differential equations. Integrating factors. Example 10.661, page 90
  4.4 problem Recognizable Exact Differential equations. Integrating factors. Example 10.701, page 90
  4.5 problem Recognizable Exact Differential equations. Integrating factors. Example 10.741, page 90
  4.6 problem Recognizable Exact Differential equations. Integrating factors. Example 10.781, page 90
  4.7 problem Recognizable Exact Differential equations. Integrating factors. Example 10.81, page 90
  4.8 problem Recognizable Exact Differential equations. Integrating factors. Example 10.83, page 90
  4.9 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.1, page 90
  4.10 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.2, page 90
  4.11 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.3, page 90
  4.12 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.4, page 90
  4.13 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.5, page 90
  4.14 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.6, page 90
  4.15 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.7, page 90
  4.16 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.8, page 90
  4.17 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.9, page 90
  4.18 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.10, page 90
  4.19 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.11, page 90
  4.20 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.12, page 90
  4.21 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.13, page 90
  4.22 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.14, page 90
  4.23 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.15, page 90
  4.24 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.16, page 90
  4.25 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.17, page 90
  4.26 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.18, page 90
  4.27 problem Recognizable Exact Differential equations. Integrating factors. Exercise 10.19, page 90