69.27 Chapter 3 (Systems of differential equations). Section 20. The method of elimination. Exercises page 212

69.27.1 problem 776
69.27.2 problem 777
69.27.3 problem 778
69.27.4 problem 779
69.27.5 problem 780
69.27.6 problem 781
69.27.7 problem 782
69.27.8 problem 783
69.27.9 problem 784
69.27.10 problem 785
69.27.11 problem 786