pde questions

All these questions are in the exercise of the book, and the book is in the attachment. There are total 9 questions:

Page 169, problems 6.7, 6.9,

Page 171, Problem 6.17, 6.18(a), 6.20(a)

Pages 204- 205, Problems 7.4, 7.5, 7.8, 7.12