Math Problem Solving: Calculus and Critical Points, Exams of Calculus

A series of math problems involving limits, directional derivatives, tangent planes, and critical points. Students are required to calculate limits, find directional derivatives, determine equations for tangent planes, and evaluate functions. The problems also involve using the chain rule and determining the nature of critical points.

Typology: Exams

Pre 2010

Uploaded on 09/02/2009

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MATH 241: TEST 2
Name
Instructions and Point Values:
Put your name in the space provided above. Work
each problem below and show ALL of your work. You do not need to simplify your answers.
Do NOT use a calculator.
Problem (1) is worth 12 points.
Problem (2) is worth 14 points.
Problem (3) is worth 14 points.
Problem (4) is worth 14 points.
Problem (5) is worth 14 points.
Problem (6) is worth 16 points.
Problem (7) is worth 16 points.
(1) Let
f
(
x; y
)=
x
3
y
x
4
+
y
4
:
Does lim
(
x;y
)
!
(0
;
0)
f
(
x; y
) exist? If so, what is it? If not, why not?
(2) Let
~v
=
h
1
;
3
i
and
f
(
x; y
)=
x
2
y
+
y
2
.Calculate the directional derivative of
f
(
x; y
)
in the direction
~v
at the point (1
;
,
1).
pf3
pf4

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MATH 241: TEST 2

Name

Instructions and Point Values: Put your name in the space provided ab ove. Work each problem b elow and show ALL of your work. You do not need to simplify your answers. Do NOT use a calculator.

Problem (1) is worth 12 p oints. Problem (2) is worth 14 p oints. Problem (3) is worth 14 p oints. Problem (4) is worth 14 p oints. Problem (5) is worth 14 p oints. Problem (6) is worth 16 p oints. Problem (7) is worth 16 p oints.

(1) Let

f (x; y ) =

x^3 y x^4 + y 4

Do es lim (x;y )!(0;0)

f (x; y ) exist? If so, what is it? If not, why not?

(2) Let ~v = h 1 ; 3 i and f (x; y ) = x^2 y + y 2. Calculate the directional derivative of f (x; y )

in the direction ~v at the p oint (1; 1).

(3) Find an equation for the tangent plane to the surface x^2 2 y 2 = xy z 2 at the p oint

(4) Let R = f(x; y ) : 1  x  3 ; 0  y  2 g and

f (x; y ) =

3 for 1  x  2 ; 0  y  2

4 for 2 < x  3 ; 0  y  2 :

Evaluate

R R

R

f (x; y ) d A.

(7) Let

f (x; y ) = (3y 4 + 1)(x^2 2 x + 2) 12 y 3 + 12 y 2 :

The function f (x; y ) has 3 critical p oints. Calculate the critical p oints and indicate (with justi cation) whether each determines a lo cal maximum value of f (x; y ), a lo cal minimum value of f (x; y ), or a saddle p oint of f (x; y ).

1) FIRST CRITICAL POINT:

LOCAL MAX, LOCAL MIN, OR SADDLE PT:

2) SECOND CRITICAL POINT:

LOCAL MAX, LOCAL MIN, OR SADDLE PT:

3) THIRD CRITICAL POINT:

LOCAL MAX, LOCAL MIN, OR SADDLE PT: