67.28 Chapter 39. Critical points, Direction fields and trajectories. Additional Exercises. page 815

67.28.1 problem 39.1 (a)
67.28.2 problem 39.1 (b)
67.28.3 problem 39.1 (c)
67.28.4 problem 39.1 (d)
67.28.5 problem 39.2