# Math 121 - Homework Corrections

There are some mistakes in the book regarding homework. In some cases, the answers in the back of the book are wrong, in other cases, the problem itself is wrong. If you're sure you're doing the problem correctly, but can't seem to get the answer the back, check here first. It's possible that there are other problems than what I've caught here.

## Corrections to Book

• 2.4.15. The book has δ = 1/505, but it should be δ = 1. Other values may work as well.
• 3.6.13. The solution is missing a square root in the numerator. It should be .
• 4.8.13. The textbook solution used the wrong function, so pretty much all the answers are wrong. Here are the answers for the position function in the book.
• v(t) = 3t2 - 6t = 3t(t - 2), a(t) = 6t - 6 = 6(t - 1)
• s(1) = -2 ft, v(1) = -3 ft/s, speed(1) = 3 ft/s, a(1) = 0 ft/s2
• The particle is stopped when v(t) = 0, which is at t = 0 s and t = 2 s.
• The particle is speeding up when v(t) and a(t) are the same sign, 0 s < t < 1 s, and t > 2 s. The particle is slowing down when v(t) and a(t) have opposite signs, 1 s < t < 2 s.
• The total distance traveled during the interval 0 s < t < 5 s is determined by breaking the function where velocity changes signs. | v(2) - v(0) | + | v(5) - v(2) | = | -4 - 0 | + | 50 - (-4) | = 4 + 54 = 58 ft.
• 5.3.29. The integral should be with respect to y, not with respect to x.
• 6.8.13. The solution should be 14,976 √17 lbs, which is approximately 61,748 lbs.

There are two homework assignments based on the skills that you need to get into this class. The problems and the solutions are given below.