Multivariable Functions: Finding Domains and Level Curves, Study notes of Calculus

Instructions and examples for finding the domains and level curves of multivariable functions. It includes several functions with their corresponding level curves and surface plots, as well as practice problems for students to solve. The document also discusses the concept of level surfaces and their relationship to multivariable functions.

Typology: Study notes

Pre 2010

Uploaded on 08/16/2009

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Introduction to Multivariable Functions
Page 1 of 4
Domains๎˜ƒof๎˜ƒMultivariable๎˜ƒFunctions๎˜ƒ
Consider the function
()
22
,9
f
xy x y=โˆ’โˆ’
.
What are the values of
()
2,1fโˆ’
and
(
)
6, 2f
โˆ’
?
Find the domain of
()
,
f
xy
and sketch the domain onto
Figure 1.
Find the domain of the function
(
)
(
)
1
,sin 2gxy x y
โˆ’
=โˆ’+
and sketch the domain onto
Figure 2.
Fi
g
ure 1
Fi
g
ure 1
pf3
pf4
pf5
pf8
pf9

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Introduction to Multivariable Functions

Domains of Multivariable Functions

Consider the function ( )

2 2 f x y , = 9 โˆ’ x โˆ’ y.

What are the values of f ( โˆ’2,1 )and f ( 6, โˆ’ 2 )?

Find the domain of f ( x y , ) and sketch the domain onto

Figure 1.

Find the domain of the function

1 g x y , sin x y 2

โˆ’ = โˆ’ + and sketch the domain onto

Figure 2.

Figure 1

Figure 1

Introduction to Multivariable Functions

Find the domain of (^) ( ) (^) ( ) ( ) (^) ( )

2 1 1 2 2 h x y , ln x 4 cos x y tan x y 4

โˆ’ โˆ’ = โˆ’ + + โˆ’ + โˆ’ and sketch the

domain onto Figure 3.

What does the domain of the function (^) ( ) 2 2 2

f x y z

x y z

look like?

Practice on finding domains of multivariable functions

Find and sketch the domain of each of the following functions.

a. (^) ( ) ( )

f x y , sin ln x 2 y x

โˆ’ โŽ›^ โŽž

b. (^) ( ) ( )

2 1 2 2 f x y , x 1 cos x y 1

โˆ’ = โˆ’ โˆ’ + โˆ’

c. ( )

2 f x y , = โˆ’ x y + x โˆ’ y

Figure 3

Introduction to Multivariable Functions

Level surfaces of Multivariable Functions

The temperature (degrees Calvin) at a point inside a vat of grease is given by the formula

z T x y z x y

. The axis system for the vat has been set up so that one corner of the vat

corresponds to the point ( 2, 2,2) and all points in the vat have coordinates that are each greater

than 2.

A level surface, (^) w = k , for this function is the set of all points in the vat that satisfy

T ( x y z , , )= k. Contextual these level surfaces are called isothermal surface.

What is the shape of the isothermal surfaces in this vat?

Finding Domains, Level Curves, Surface Plot worksheet

z sin x

โˆ’ โŽ›^ โŽž

2 z = x โˆ’ 1

y z

x

z = ln ( y โˆ’ x )

( )

1 z cos x y

โˆ’ = +

2

2

ln

x z

y

  • Figure
  • Figure 11 Figure
  • Figure 9 Figure
    • Figure

x

y

x

y

Figure 1: Level Curves: z =3, 2,1, 0 Figure 2: Level Curves: z = 2,1, 0, โˆ’ 1

Figure 3: Level Curves: z = 2,1, 0, โˆ’ 1 Figure 4: Level Curves: z =3, 2,1, 0

x

y

x

y

Figure 5: Level Curves:

z = โˆ’ โˆ’ Figure 6: Level Curves: z =3, 2,1, 0

x

y

x

y