9/15/2016 Minor changes for clarity to the text before example 13.2.7
(late transcendentals 15.2.7) and to the example.
9/25/2016 Added theorem 14.3.5 (16.3.5)
10/ 9/2016 Minor corrections in 14.5 & 14.7 (16.5 & 16.7)
equation -> vector function in a few exercises in 14.5
added one displayed equation in example 14.7.2
10/30/2016 Correct answer to 9.8.3 (11.3.3): answer was variance, but
standard deviation was required.
Change a w to w' in section 15.7 (17.7)
10/31/2016 Section 4.3, change "we don't have to a similar calculation"
to "we don't have to do a similar calculation"
11/15/2016 Fixed minor typo in example 16.5.3 (18.5.3).
11/17/2016 Fixed a minor typesetting problem in exercise 16.5.9 (18.5.9).
11/23/2016 Fixed answer to 10.3.12 (12.3.12).
11/29/2016 Changed y>0 to y\ge0 in exercise 16.7.11 (18.7.11).
Added hint to exercise 16.8.7 (18.8.7).
12/ 5/2016 Clarify exercise 16.6.8 (18.6.8) to say b\le a.
12/ 9/2016 Clarify "counterclockwise" rule for Stokes's theorem in
16.8 (18.8).
12/16/2016 Add answer to 12.1.10 (14.1.10)