Differential Equations

Math 23 Fall 2020

Homework

Homework reinforces concepts and skills while challenging students to extend what they have learned to other types of problems. Because it is important for students to have this experience, instructors will not solve assigned homework problems during office hours before the due date. We will of course answer questions you may have in approaching problems that give you difficulty. It is therefore essential to begin homework sets early so that you may get help if difficulties do arise.

It is due each Tuesday before midnight (East coast time). We will be using webwork . As all homework is posted well in advance, no late homework will be accepted.

Homework grading policy: The goal of homework is to learn to work through problems. Therefore each problem set will be assigned a grade on a 10 point scale based on the following percentage of correct results as submitted through webwork: 85% or higher = 10; 81-85% = 9; 71-80% = 8; 61-70% = 7; 50-60% = 6; 30-49% = 5; 20-29% = 3; 10-19% = 2; 5-9% = 1; below 5% = 0. The lowest homework score will be dropped, and the combination of the remaining scores will be scaled according to the 100 point grading scheme.

Cooperation on homework is both permitted and encouraged, but your final solutions should be your own. We have included a list of problems assigned in previous terms. They are not to be turned in, but will be useful in ensuring that you are following the material.

Week Suggested Book Problems
Week 2 §1.1: #7, 9, 12, 22, 24
§1.2: #5, 12 (Hint: do (b) first), 13
§1.3: #8, 14
§2.1: #15, 17, 30, 33
§2.2: #8, 18, 25
§2.4: #11, 14, 22, 25, 28, 33
Week 3 §2.3: #2, 4, 8 (Hint: Solve 8 (c) numerically.), 15
§2.5: #4, 12, 15
§2.6: #2, 14, 16, 24, 27
Use exercise 24 in 2.6 to solve the equation $$(3y^2 + 4xy) + (4xy + 3x^2) \frac{dy}{dx} = 0.$$
Week 4 §3.1: # 11, 22, 23, 27
§3.2: # 10, 19, 22, 27, 34
§3.3: # 5, 11, 20, 26, 35
Week 5 §3.4: # 6, 13, 28
§3.5: # 9, 14, 18, 29
§3.6: # 11, 15
§7.1: # 7, 15
§7.3: # 11, 25
§7.4: # 2 (only (a), (b), (c)), 5, 6 (only (a), (b))
Week 6 §7.5: # 8, 18, 25, 29
§7.6: # 10, 11, 28
§7.8: # 10, 15, 18 (only (a), (b), (c), (d)
Week 7 §9.1: # 18, 20, 21
§9.1: # 15
§7.9: # 2, 4, 12, 14
Week 8 §9.2: # 4, 8, 25
§9.3: # 4, 9, 20, 27
§9.4: # 3, 8
§9.5: # 4, 12

Plotting slope fields and trajectories
Direction field plotter
Week 9 §6.1 # 2, 14, 24
§6.2 # 16, 26, 29, 32
§6.3 # 18, 20, 25 §6.4 # 8, 17
§6.5 # 8, 14, 18
§6.6 # 1, 2, 16, 21