KEY
Math 126: Quiz 6
December 9, 2015
You have the remainder of the hour to complete this closed-book, closed-notes,
closed-colleague quiz. You may use a calculator for arithmetic only (ie, no plotting).
PLEASE READ ALL DIRECTIONS CAREFULLY!
1. Find the length of the curve y = 3 + 2z) from (1,5) to (4, 19)
= 7"93"1."
= 4{37-2"7
2. (a) Find the area of the surface generated by rotating the portion of the curve
y - 2' between 1 = 0 and I - 3 about the r-axis.
5.1. = Saands
* 5.20 2' 1329 de = S2ox Magerde
$ 19(0)": /
+1 = 1+ 9(3) - 730
→ SA: 26
(b) Set up, but don't evaluate, the integral for the surface area generated by
rotating that same portion of the curve about the y-axis.
or
3. Find the value, if it exists, of
e"du
lim
6-100
du=-2+dy
2 6-100
te"]
= 0*2 = 2
4. Without calculating, would you expect
5/2
to converge or diverge, and why?
Drege. It behaves like a pinkyal
w.h p= 12«1.
5. Suppose that we have society that elects 1200 new members each year. In
addition, the society loses 15% of its members each year.
(a) Give a differential equation for the membership M as it changes relative
to time t.
dM
= 1200-, 15M
dt
M= 8000+ Be''t
:: 15 (M -8000)
d t
(b) If there are 3000 members to begin with, how many will there be after 3
years?
MCO) = 2000 = B = 8000-8000 = 5000
M= 8000-5000 € : ist
M13) = 8000-5000 € 45 = 4811
(c) If there are 3000 members to begin with, how many will be in the society
long-term?
lany ter → 8000 as the constant Deps off
(d) If there are 10,000 members to begin with, how many will there be in the
society long-term?
10000 stent
BLt) = 8000 +2000 € 156
→ B → 8000 sh/l
6. A pair of species exist on an island and are competing for the same limited
(but renewable) resource for survival. The differential equations governing the
system are as follows.
dA
=TA+ siA?+ tAB
dt
d.B
- = rzB + s2B? + bAB
dt
Are the constants (1, 51, t1, 72, 82, tz) positive or negative? Explain your rea-
soning biologically.
r, re 70 → These follow a lays tie pattem.
to ta <0 = Whenbospecies ane present.
it adversely affects
botrpoplations!
7. Which concepts are you most comfortable about heading into the final? Where
do you need the most work?