Harvard University,FAS
Spring 2006

Mathematics Math21a
Spring 2006

Multivariable Calculus

Course Head: Oliver Knill
Office: SciCtr 434
Email: knill@math.harvard.edu
Harvard Mathematics

Weekly checklists [PDF]: "Somewhere, over the rainbow ..."
Week1 Week2 Week3 Week4 Week5 Week6 Week7 Week8 Week9 Week10 Week11 Week12

Homework

All sections have the same homework during weeks 1-10. Biochem homework will be different in weeks 11-12.
  • Homework is due at the beginning of class. The last homework in the semester will be due Tuesday morning 11 AM latest in the mailbox of the CA.
  • 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.
  • 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 9.1: 8,10,14,18,34           Due Wed Feb 8    (rsp Thu Feb 9 for TTh)
2. Class 9.2: 18,26,38  9.3: 34,38    Due Fri Feb 10   (rsp Tue Feb 14 for TTh)
3. Class 9.4: 6,14,16,30,34           Due Mon Feb 13   (rsp Tue Feb 14 for TTh)
 Solutions 
Week 2:

1. Class 9.5: 8,30,36,48,54           Due Wed Feb 15   (rsp Thu Feb 16 for TTh)
2. Class 9.6: 2,4,10,18,24            Due Fri Feb 17   (rsp Tue Feb 21 for TTh)
3. Class 9.6: 12,22,34                Due Wed Feb 22   (rsp Tue Feb 21 for TTh)
         Problem A: The global positioning system GPS is based on the fact
         that a receiver can easily find the difference of distances
         to two satellites (each GPS satellite sends periodically signals which
         are triggered by an atomic clock. While the distance to each satellite
         is not known, the difference from the distances to two satellites can be determined from 
         the time delay of the two signals. The receiver does not need an atomic clock). 
         Given two satellites P=(2,0,0), Q= (0,0,0) in
         space. Identity the quadric, whose distance to P is by 1 larger than 
         the distance to Q. How many GPS satellites does your GPS receiver have to "see"
         in space so that it can determine the position?
         Problem B: Find the surface whose points have the property that
         the distance to the x-axes is half the distance to the parametrized line 
         r(t) = (1,0,0) + t (0,0,1).  
 Solutions ,
Problem A,
Problem B.
Week 3:

1. Class  10.1: 16,32,38   10.2: 28,46   Due Fri Feb 24 (rsp Thu Feb 23 for TTh)
2. Class  10.3: 4,14,18    10.4: 24,38   Due Mon Feb 27 (rsp Tue Feb 28 for TTh)
Solutions ,
Week 4:

1. Class 9.7:   10,16,20,28,36           Due Wed Mar 1 (rsp Thu Mar 2 for TTh)
2. Class 10.5:  4,18,28,30,32            Due Fri Mar 3 (rsp Tue Mar 7 for TTh)
3. Class 11.1: 16,22,31-36   11.2: 30,36 Due Mon Mar 6 (rsp Tue Mar 7 for TTh)

 Solutions 
Week 5: 

1. Class: 11.3:64,66,68,80 (d optional)              Due Wed Mar 8 (rsp Thu Mar 9)
          A: Verify that f(x,t)=e(-r t) sin(x+ct)
          satisfies the advection equation
          ft(x,t) = c fx(x,t) - r f(x,t).
2. Class: 11.4: 4,6,26,30,32                         Due Fri Mar 10 (rsp Tue Mar 14)
3. Class: 11.5: 4,26,28,32,42                        Due Mon Mar 13 (rsp Tue Mar 14)

 Solutions
Week 6:

1. Class: no homework (exam)
2. Class: 11.6: 24,42,44,46, A
     A: r(u,v) = (u,v3,u3+v2) is a parametrized surface S.
        a) Find an implicit equation g(x,y,z)=0 for this surface.
        b) Use a) to find the tangent plane at the point (1,1,2).
        c) Why are the vectors ru(u,v) and rv(u,v) tangent to S?
        d) Use c) to find the tangent plane at the point (1,1,2) again.
                                                     Due Friday, Mar 17 rsp. Tue Mar 21
3. Class: 11.6: 10,26,28,30,36                       Due Monday, Mar 20 rsp. Tue Mar 21

 Solutions
Week 7: 

1. Class: 11.7: 2,12,44,48,50                    Due Wednesday Mar 22 rsp Thursday Mar 23
2. Class: 11.8: 4,6,10,16,38                     Due Friday    Mar 24 rsp Thuesday Apr  4
3. Class: 11.8: 18, 24, review page 827: nr 8    Due Monday    Apr 3  rsp Tuesday  Apr  4
      A:  Find the extrema of the function 
          f(x,y) = (x2+2y2 ) exp(-x2 -y2) on the
          circle g(x,y)=x2+y2=4 
          using the method of Lagrange multipliers. 
      B:  Find the absolute maximum of the same function f inside 
          { x2+y2 less or equal to 4 }.
Solutions
Week 8:

1. Class: 12.1: 8, 12.2: 8,10,14,32          Due Wed Apr 5  rsp Thu Apr  6
2. Class: 12.3: 4,26,36,42,44                Due Fri Apr 7  rsp Tue Apr 11
2. Class: 12.4: 8,20,24,28,30                Due Mon Apr 10 rsp Tue Apr 11

 Solutions
Week 9:

1. Class: 12.5: 22, 12.6: 14,24,26,28        Due Wed Apr 12  rsp Thu Apr 13
2. Class: 12.7: 4,12,32,44,48                Due Fri Apr 14  rsp Tue Apr 15
3. Class: 12.8: 4,8,16,32,36                 Due Mon Apr 17  rsp Tue Apr 15

 Solutions
Week 10:

1. Class: no homework (exam)
2. Class: 13.1: 10,11-14,15-18,24,34         Due Fri Apr 21  rsp Tue Apr 22
3. Class: 13.2: 12,18,20,34,42               Due Mon Apr 24  rsp Tue Apr 22

 Solutions
Bio chem section:

2. Class: p.10-12 #1,4,6,7 p.22-24 #5,9,14   Due Fri Apr 21
3. Class: p.22 #3,12,17, p.34 #1,4,6         Due Mon Apr 24

 Solutions 
Week 11:

1. Class: 13.3: 8,16,22,26,32                Due Wed Apr 28 rsp Thu Apr 29
2. Class: 13.4: 6,8,12,14,18                 Due Fri Apr 31 rsp Tue May  2
3. Class: 13.5: 6,10,16,27,36                Due Mon May  1 rsp Tue May  2
Solutions
Bio chem section:

1. Class  p. 35: 3, 5, 14                   Due Wed
          p. 50: 1, 4
2. Class  p. 50: 7, 9, 11, 12, 14           Due Fri

3. Class  p. 50: 5, 16, 17, 20              Due Mon
Solutions
Week 12:

1. Class: 13.6:  20,22,26,40,42 
2. Class: 13.7:  4,8,10,14,18   
3. Class: 13.8:  2,10,26  13.9: 34,38       Due Tue in reading period

 Solutions 12.8
 Solutions 12.9
Bio chem section:

1. Class:  p.65 #2, 3, 8, 13

Monty Hall Problem :  A contestant plays the following game. He or  
she is presented with three doors. Behind one door is a prize and
behind the other two doors are goats. We assume that the contestant
refers the prize to the goat. The contestant picks a door behind
which he or she expects to find the prize. Monty Hall, the game show  
host (who knows where the prize is), opens one of the two other
unpicked doors, revealing a goat. The contestant is now given the
option of switching his or her choice to the other closed door.

(a) Should the contestant switch?
(b) What if Monty Hall does not know where the prize is but picked a
random door which happened to have a goat beind it?
2. Class:
(1) Three cards are chosen from three different decks. What is the probability of getting at least one spade? (2) In a poker hand, John has a very strong hand and bets 5 dollars. The probability that Mary has a better hand is .04. If Mary had a better hand she would raise with probability .9, but with a poorer hand she would only raise with probability .1. If Mary raises, what is the probability that she has a better hand than John does? (3) When playing bridge, what is the probability that each of the four players receives an ace? Why is the following argument wrong? "It does not matter where the first ace goes. The second ace must go to one of the other three players and this occurs with probability 3/4. Then the next must go to one of two, an event of probability 1/2, and finally the last ace must go to the player who does not have an ace. This occurs with probability 1/4. The probability that all these events occur is the product (3/4)(1/2)(1/4) = 3/32." (4) Let U, V be random numbers chosen independently from the interval [0, 1]. Find the probabity density, distribution function, expected value and variance of the following random variables.

(a) Y = max(U, V ).
(b) Y = min(U, V ).
3. Class Problems PDF Solutions


Please send comments to math21a@fas.harvard.edu
Math21a, Multivariable Calculus, Spring 2006, Department of Mathematics, Faculty of Art and Sciences, Harvard University


Fri May 26 21:44:46 EDT 2006