69.13 Chapter 2 (Higher order ODEs). Section 13. Basic concepts and definitions. Exercises page 98

69.13.1 problem 318
69.13.2 problem 319
69.13.3 problem 320
69.13.4 problem 321
69.13.5 problem 322
69.13.6 problem 323
69.13.7 problem 324
69.13.8 problem 325
69.13.9 problem 326