Exam II - November 6, 2007, Multivariable Calculus, Prof. P. Wong, Exams of Mathematics

The solutions to exam ii of the multivariable calculus course taught by prof. P. Wong, held on november 6, 2007. The exam covers topics such as continuity, vector calculus, directional derivatives, critical points, and surface integrals.

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MATH206A MULTIVARIABLE CALCULUS - PROF. P.
WONG
EXAM II - NOVEMBER 6, 2007
NAME:
Instruction: Read each question carefully. Explain ALL your work and
give reasons to support your answers.
Advice: DON’T spend too much time on a single problem.
Problems Maximum Score Your Score
1. 15
2. 20
3. 15
4. 20
5. 15
6. 15
Total 100
1
pf3
pf4
pf5

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MATH206A MULTIVARIABLE CALCULUS - PROF. P.

WONG

EXAM II - NOVEMBER 6, 2007

NAME:

Instruction: Read each question carefully. Explain ALL your work and give reasons to support your answers. Advice: DON’T spend too much time on a single problem.

Problems Maximum Score Your Score

  1. 15
  2. 20
  3. 15
  4. 20
  5. 15
  6. 15 Total 100

1

2 EXAM II - NOVEMBER 6, 2007

1.(7 pts) (i) Consider the function

f (x, y) =

3 xy x^4 +y^2 ,^ if (x, y)^6 = (0,^ 0); 0 , otherwise.

Determine whether f (x, y) is a continuous at (0, 0). Justify your answer. [Hint: try approaching (0, 0) from different directions]

(8 pts.)(ii) Consider the vector field F (x, y, z) = (2xz, −xy, −z). Find div F and curl F.

4 EXAM II - NOVEMBER 6, 2007

  1. Let f (x, y) = x^2 e−^2 y. (7 pts) (i) Find the directional derivative Duf (1, 0) of f at the point (1, 0) in the direction of u = i + j.

(8 pts) (ii) Find an equation for the line tangent to the level curve f (x, y) = 1 at the point (1, 0).

MATH206A MULTIVARIABLE CALCULUS - PROF. P. WONG 5

  1. Consider the function f (x, y) = x^3 + y^3 + 3x^2 − 3 y^2. (4 pts) (i) Find all the critical points of f.

(8 pts) (ii) For each of the critical point(s) a found in part (i), find the corresponding Hessian matrix Hf (a).

(8 pts) (iii) Use the second derivative test to classify each of the critical point(s) in part (i), i.e., determine whether the critical point is a local max, local min, or saddle point.

MATH206A MULTIVARIABLE CALCULUS - PROF. P. WONG 7

  1. Let C be the arc of the unit circle from (1, 0) to (0, 1) and F (x, y) = (x, x^2 + y^2 ). (6 pts.) Write a parametrization x(t) for the curve C. Be sure to state the range of the parameter.

(9 pts.) Find the work done by the force F over the curve C. That is, find

C F^ (x)^ ·^ dx.