Homework
 Homework is due at the beginning of class.
We do not accept electronic HW submission. If you do the homework
with a word processor like LateX, print it out and submit the paper.
 Please staple your homework.
 No late homework accepted but will delete the least 3 scores
for MWF sections and 2 for TTh sections.
Reserve these 3 "Joker" cards for emergencies.
 Collaborations are welcome however you must turn in your
own copy and list on it the names of your collaborators.
 Similarly, acknowledge the use of Mathematica. If you use Mathematica,
nevertheless, write down all steps of your computation.
 If you can not turn in your homework because of a religious holiday
like Yom Kipur, turn it in earlier or give it to a friend
to turn it in.
 Homework scores from individual sections will be adjusted in the end
because different graders grade each section.

 Please write legibly and indicate clearly, where a new problem starts.
 Try to keep the problems in order.
 Use words to explain your work, if necessary. Show your work.
 If unable to finish a problem, indicate where you are
stuck. This will help us to give partial credit.
 Please infom about typos, misprints. We state here corrections
to the in class distributed texts as well as to the posted solutions.
Each hint gives you a bonus point. The texts posted here are corrected.
 (+Sol) means solutions have been posted.
Solution folder (in case, solutions are not yet linked).

Week 1:
1. Class: 11.2: 8,12,20,58,60 Due Wed (rsp Thu for TTh)
2. Class: 11.1: 34,36, 11.2: 76, 11.3: 20, 62 Due Fri (rsp Tue for TTh)
3. Class: 11.4: 8, 18, 38, 48, 54 Due Mon (rsp Tue for TTh)
Solutions

Week 2:
1. Class: 11.5: 16,20,40,64 (find distance),66 Due Wed (rsp Thu for TTh)
2. Class: 12.1: 26, 62 12.2: 12, 34, 50 Due Fri (rsp Tue for TTh)
3. Class: 12.3: 12,14,42, 56, 58 Due Wed (rsp Tue for TTh)
Solutions

Week 3:
1. Class: Happy Columbus day!
2. Class: 12.4: 10, 46, 13.1: 38, 46, 64 Due Fri (rsp Thu for TTh)
3. Class: 13.2: 16,22,26,28, 32 Due Mon (rsp Tue for TTh)
Solutions

Week 4:
1. Class: No Homework from Monday to Wednesday or Tuesday to Thursday
2. Class: 14.8: 4,10,19. There are additional custom problems:
Problem A) invent a surface rho = f(phi,theta), simple enough
to draw, but not in the book.
Problem B) invent a surface r = g(theta,z), simple enough
to draw but not appear in the book. You can use technology to
play with but it is fine (probably even better), if you tackle
the problem eventually without it. See FAQ.
3. Class: This problem is a custom problem set due Monday or Tuesday in the 5th week:
A) Parametrize the upper half of the
ellipsoid x^{2}+y^{2}+z^{2}/4=1 in three different
ways: as a graph r(u,v) = (u,v,f(u,v)) (Euclidean coordinates), as a surface of revolution
r(theta,z) = (g(z) cos(theta),g(z) sin(theta),z) (cylindrical coordinates) and as a
deformed sphere r(phi,theta) = (x(phi,theta), y(phi,theta), z(phi,theta) ) (spherical coordinates).
B) The curve r(t) = (t^{1/2} cos(t), t^{1/2} sin(t), t)
can be placed on a surface. Find a parametrization r(t,s) of this surface.
C) Parametrize the surface which has distance 1 from the unit circle in the xy plane.
This is a doughnut. Use two angles.
D) Parametrize the paraboloid x^{2} + y^{2} = z in two different ways:
as a graph or as a surface of revolution.
E) Upload a picture for a gallery of marbles
here
Solutions

Week 5:
(We use frequently the notation f_{x}(x,y) for the partial
derivative of f(x,y) with respect to x).
1. Class 13.3: 10, 14. 13.4: 20, 32, 50
2. Class 13.4: 14, 52, 60,
Problem A: verify that for any function g(x) of one variable,
the function f(x,y) = g(xy) + g(x+y) is a solution to the
wave equation f_{xx}(x,y) = f_{yy}(x,y).
Problem B:
Cobb and Douglas found in 1928 empirically a formula
P(L,K)= r L^{a} K^{b} for the total production P
of an economic system as a function of the amount of labour L
and the capital investment K. By fitting data, they got
r=1.01, a=0.75, b=0.25. Verify that the function P(L,K) satisfies the
partial differential equation L P_{L} + K P_{K} = P.
3. Class: 13.5: 2,6, 12, 44, 46
hint to 44
Solutions

Week 6:
1. Class 13.6: 2,8 13.7: 40, 42, Problem A: given g(x,y,z) = zf(x,y). What is the relation
between the gradient of g, a vector in space and the gradient of f, a vector in the plane?
Describe it in general and explain it also with a simple example, where you can draw the level
curves of f and the level surfaces of g.
2. Class 13.6: 20, 26, 48, 52, 56
3. Class 13.7: 12, 16, 30, 34, 38
(In problem 34, the "hypothenuse" is the base of the triangle.)
Solutions

Week 7:
1. Class: 13.8: 2, 18, 20, 30, 40
Problem 30: look for a minimum, not a maximum
2. Class: 13.9: 4,12,28,24,34
3. Class: no class: Veterans day
Solutions

Week 8:
1. Class no homework (exam review)
2. Class: 14.1: 18, 44 14.2: 24,26 14.3: 26 Due: Friday, rsp Tuesday
3. Class: 14.5: 8,10, 30,54,60 Due: Monday, rsp Tuesday
Solutions

Week 9:
1. Class: 14.6: 8, 24,26, 36, Due Wednesday Nov 22 rsp Tuesday Nov 28
Problem 42 is deleted now
2. Class: 14.7: 2, 8, 16, 18, 20 Due Monday rsp Tuesday (after thanksgiving)
3. Class: no homework (thanksgiving)
Solutions

Week 10:
1. Class: 14.8 26,28,30, 32, 36
2. Class: 15.1: 6, 20, 26, 28, 48
(in 6 and 48 also draw some flow lines)
3. Class: 15.2: 2,6,20,38,40
Solutions and
Solutions Addendum

Week 11:
1. Class: 15.3: 10,12,22,34,40
2. Class: 15.4: 8,20,28,34,42
3. Class: 15.5: 6,10,12,26,28
Solutions

Week 12:
1. Class: 15.6: 16 Problem A: compute the surface area of the
surface r(u,v) = < v cos(u), v sin(u), v^{2} >, with u from 0 to Pi/2
and v from 0 to 1. 15.7: 28, 30 (compute only the flux integral),
Problem B: compute the flux of F(x,y,z) = (0,0,z) through the torus
parametrized as
r(u,v) = < (2+cos(v)) cos(u), (2+cos(v)) sin(u), sin(v)>,
where both u and v range from 0 to 2pi.
Problem 15.7:32: delete =2 in the definition of the surface.
The surface is the elliptic paraboloid z= 1x^{2}/4y^{2}, z>0
2. Class: 15.7: 14,16,18,32, Problem A: Find the flux of the curl of
F(x,y,z) = <y + x y z, sin(x y z), sin(cos(x y  z))>
through the upper half of the sphere
x^{2} + y^{2} + z^{2} =1, z > 0.
The surface is oriented upwards. }
3. Class: 15.8: 2,10b,18b, Problem A:
Use the divergence theorem to calculate the flux
of F(x,y,z) = (x^{3},y^{3},z^{3}) through the sphere
x^{2}+y^{2}+z^{2}=1. The sphere is oriented outwards.
Problem B: What is the flux of the vector field
F(x,y,z) = < sin(y) cos(z), sin(z) cos(x), sin(x) cos(y) >
through the torus surface parametrized by
r(u,v) = < (2+cos(v)) cos(u), (2+cos(v)) sin(u), sin(v) >
where both u and v range from 0 to 2pi?
Solutions

