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 Suppose [math], [math] and [math].

A. Find the gradient of f.
[math]  [math]  [math]
Note: Your answers should be expressions of x and y; e.g. "3x - 4y"

B. Find the gradient of f at the point P.
[math]  [math]  [math]
Note: Your answers should be numbers

C. Find the directional derivative of f at P in the direction of [math].
[math] 
Note: Your answer should be a number

D. Find the maximum rate of change of f at P.

Note: Your answer should be a number

E. Find the (unit) direction vector in which the maximum rate of change occurs at P.
[math]  [math]  [math]
Note: Your answers should be numbers

Note: You can earn partial credit on this problem.

 

For each of the following pairs of functions [math] and [math], determine if the level curves of the functions cross at right angles, and find their gradients at the indicated point.

(a) [math], [math].
Do the level curves of [math] and [math] cross at right angles? 
[math] 
[math] 

(b) [math], [math].
Do the level curves of [math] and [math] cross at right angles? 
[math] 
[math] 

  Use the contour diagram of [math] to decide if the specified directional derivative is positive, negative, or approximately zero.

  1. At the point [math] in the direction of [math],

  2. At the point [math] in the direction of [math],

  3. At the point [math] in the direction of [math],

  4. At the point [math] in the direction of [math],

  5. At the point [math] in the direction of [math],

  6. At the point [math] in the direction of [math],

 

(Click graph to enlarge)

Note: You can earn 50% partial credit for 4 - 5 correct answers.

Each diagram represents the level curves of a function. For each function, consider the point above [math] on the surface [math].

(a) If the vectors below are normal to the surface at the point [math], match each vector to a diagram.

  1. [math]

  2. [math]

  3. [math]

  4. [math]


(b) If the equations below are tangent planes to the surface at the point [math], match each equation of the plane to a diagram.

  1. [math]

  2. [math]

  3. [math]

  4. [math]

 
 
 
A   B
 
 
 
C   D
 
(Click on a graph to enlarge it)

Note: You can earn 50% partial credit for 4 - 5 correct answers, and 75% partial credit for 6 - 7 correct answers.

 

 If the gradient of [math] is [math] and the point [math] lies on the level surface [math], find an equation for the tangent plane to the surface at the point [math].

[math] 

 

Consider the function

[math]
(a) Find [math].
[math] 

(b) Find a function [math] whose level zero set is equal to the graph of [math] and such that the coefficient of [math] in [math] is [math].
The level set [math]  [math] is the same as the graph of [math].

(c) Find the gradient of [math]. Write your answer as a row vector of the general form [math].
[math] 

(d) Use [math] to find a vector [math] perpendicular (or normal) to the graph of [math] at the point [math]. Write your answer as a row vector of the general form [math].
[math] 

(e) Find an equation for the tangent plane to [math] at the point [math]. Enter your answer as an equation.

Note: You can earn partial credit on this problem

 

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