<< Chapter < Page Chapter >> Page >

Evaluating an improper double integral in polar coordinates

Evaluate the integral R 2 e −10 ( x 2 + y 2 ) d x d y .

This is an improper integral because we are integrating over an unbounded region R 2 . In polar coordinates, the entire plane R 2 can be seen as 0 θ 2 π , 0 r .

Using the changes of variables from rectangular coordinates to polar coordinates, we have

R 2 e −10 ( x 2 + y 2 ) d x d y = θ = 0 θ = 2 π r = 0 r = e −10 r 2 r d r d θ = θ = 0 θ = 2 π ( lim a r = 0 r = a e −10 r 2 r d r ) d θ = ( θ = 0 θ = 2 π d θ ) ( lim a r = 0 r = a e −10 r 2 r d r ) = 2 π ( lim a r = 0 r = a e −10 r 2 r d r ) = 2 π lim a ( 1 20 ) ( e −10 r 2 | 0 a ) = 2 π ( 1 20 ) lim a ( e −10 a 2 1 ) = π 10 .
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Evaluate the integral R 2 e −4 ( x 2 + y 2 ) d x d y .

π 4

Got questions? Get instant answers now!

Key concepts

  • To apply a double integral to a situation with circular symmetry, it is often convenient to use a double integral in polar coordinates. We can apply these double integrals over a polar rectangular region or a general polar region, using an iterated integral similar to those used with rectangular double integrals.
  • The area d A in polar coordinates becomes r d r d θ .
  • Use x = r cos θ , y = r sin θ , and d A = r d r d θ to convert an integral in rectangular coordinates to an integral in polar coordinates.
  • Use r 2 = x 2 + y 2 and θ = tan −1 ( y x ) to convert an integral in polar coordinates to an integral in rectangular coordinates, if needed.
  • To find the volume in polar coordinates bounded above by a surface z = f ( r , θ ) over a region on the x y -plane, use a double integral in polar coordinates.

Key equations

  • Double integral over a polar rectangular region R
    R f ( r , θ ) d A = lim m , n i = 1 m j = 1 n f ( r i j * , θ i j * ) Δ A = lim m , n i = 1 m j = 1 n f ( r i j * , θ i j * ) r i j * Δ r Δ θ
  • Double integral over a general polar region
    D f ( r , θ ) r d r d θ = θ = α θ = β r = h 1 ( θ ) r = h 2 ( θ ) f ( r , θ ) r d r d θ

In the following exercises, express the region D in polar coordinates.

D is the region of the disk of radius 2 centered at the origin that lies in the first quadrant.

Got questions? Get instant answers now!

D is the region between the circles of radius 4 and radius 5 centered at the origin that lies in the second quadrant.

D = { ( r , θ ) | 4 r 5 , π 2 θ π }

Got questions? Get instant answers now!

D is the region bounded by the y -axis and x = 1 y 2 .

Got questions? Get instant answers now!

D is the region bounded by the x -axis and y = 2 x 2 .

D = { ( r , θ ) | 0 r 2 , 0 θ π }

Got questions? Get instant answers now!

D = { ( x , y ) | x 2 + y 2 4 x }

Got questions? Get instant answers now!

D = { ( x , y ) | x 2 + y 2 4 y }

D = { ( r , θ ) | 0 r 4 sin θ , 0 θ π }

Got questions? Get instant answers now!

In the following exercises, the graph of the polar rectangular region D is given. Express D in polar coordinates.

A sector of an annulus D is drawn between theta = pi/4 and theta = pi/2 with inner radius 3 and outer radius 5.

D = { ( r , θ ) | 3 r 5 , π 4 θ π 2 }

Got questions? Get instant answers now!
 A sector of an annulus D is drawn between theta = 3 pi/4 and theta = 5 pi/4 with inner radius 3 and outer radius 5.

D = { ( r , θ ) | 3 r 5 , 3 π 4 θ 5 π 4 }

Got questions? Get instant answers now!

In the following graph, the region D is situated below y = x and is bounded by x = 1 , x = 5 , and y = 0 .

A region D is given that is bounded by y = 0, x = 1, x = 5, and y = x, that is, a right triangle with a corner cut off.
Got questions? Get instant answers now!

In the following graph, the region D is bounded by y = x and y = x 2 .

A region D is drawn between y = x and y = x squared, which looks like a deformed lens, with the bulbous part below the straight part.

D = { ( r , θ ) | 0 r tan θ sec θ , 0 θ π 4 }

Got questions? Get instant answers now!

In the following exercises, evaluate the double integral R f ( x , y ) d A over the polar rectangular region D .

f ( x , y ) = x 2 + y 2 , D = { ( r , θ ) | 3 r 5 , 0 θ 2 π }

Got questions? Get instant answers now!

f ( x , y ) = x + y , D = { ( r , θ ) | 3 r 5 , 0 θ 2 π }

0

Got questions? Get instant answers now!

f ( x , y ) = x 2 + x y , D = { ( r , θ ) | 1 r 2 , π θ 2 π }

Got questions? Get instant answers now!

f ( x , y ) = x 4 + y 4 , D = { ( r , θ ) | 1 r 2 , 3 π 2 θ 2 π }

63 π 16

Got questions? Get instant answers now!

f ( x , y ) = x 2 + y 2 3 , where D = { ( r , θ ) | 0 r 1 , π 2 θ π } .

Got questions? Get instant answers now!

f ( x , y ) = x 4 + 2 x 2 y 2 + y 4 , where D = { ( r , θ ) | 3 r 4 , π 3 θ 2 π 3 } .

3367 π 18

Got questions? Get instant answers now!

f ( x , y ) = sin ( arctan y x ) , where D = { ( r , θ ) | 1 r 2 , π 6 θ π 3 }

Got questions? Get instant answers now!

f ( x , y ) = arctan ( y x ) , where D = { ( r , θ ) | 2 r 3 , π 4 θ π 3 }

35 π 2 576

Got questions? Get instant answers now!

D e x 2 + y 2 [ 1 + 2 arctan ( y x ) ] d A , D = { ( r , θ ) | 1 r 2 , π 6 θ π 3 }

Got questions? Get instant answers now!

D ( e x 2 + y 2 + x 4 + 2 x 2 y 2 + y 4 ) arctan ( y x ) d A , D = { ( r , θ ) | 1 r 2 , π 4 θ π 3 }

7 576 π 2 ( 21 e + e 4 )

Got questions? Get instant answers now!

In the following exercises, the integrals have been converted to polar coordinates. Verify that the identities are true and choose the easiest way to evaluate the integrals, in rectangular or polar coordinates.

Questions & Answers

what is biology
Hajah Reply
the study of living organisms and their interactions with one another and their environments
AI-Robot
what is biology
Victoria Reply
HOW CAN MAN ORGAN FUNCTION
Alfred Reply
the diagram of the digestive system
Assiatu Reply
allimentary cannel
Ogenrwot
How does twins formed
William Reply
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
what is genetics
Josephine Reply
Genetics is the study of heredity
Misack
how does twins formed?
Misack
What is manual
Hassan Reply
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
what is biology
Yousuf Reply
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
Joseph Reply
what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
cell is the building block of life.
Condoleezza Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 1

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Calculus volume 3. OpenStax CNX. Feb 05, 2016 Download for free at http://legacy.cnx.org/content/col11966/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Calculus volume 3' conversation and receive update notifications?

Ask