Summarize how to find the limits of integration when integrating in order dr dθ. We will typically integrate in this order.
Summarize how to find the limits of integration when integrating in order dr dθ. We will typically integrate in this order.
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Related questions
Question
Question 3: Summarize how to find the limits of
Hint 1: Read the subsection “Finding Limits of Integration” (p. 916 – 917).

Transcribed Image Text:rsin - y=√/2
or
r=√√/2csc 0
2
2
√₂
Leaves at r = 2
L
R
R
Enters at r
(b)
Largest 0 is
L
√2 csc 0
Smallest is.
>X
FIGURE 15.24 Finding the limits of
integration in polar coordinates.
A version of Fubini's Theorem says that the limit approached by these sums can be evalu-
ated by repeated single integrations with respect to r and as
8-B pr-gy(0)
f(r, 0)r dr do.
[[
f(r, 9) dA =
Finding Limits of Integration
The procedure for finding limits of integration in rectangular coordinates also works for
polar coordinates. We illustrate this using the region R shown in Figure 15.24. To evaluate
f(r, 0) dA in polar coordinates, integrating first with respect to r and then with respect
to 0, take the following steps.
1. Sketch. Sketch the region and label the bounding curves (Figure 15.24a).
2. Find the r-limits of integration. Imagine a ray L. from the origin cutting through R in the
direction of increasing r. Mark the r-values where L enters and leaves R. These are the
r-limits of integration. They usually depend on the angle that L makes with the posi-
tive x-axis (Figure 15.24b).
3. Find the 0-limits of integration. Find the smallest and largest 9-values that bound R.
These are the 0-limits of integration (Figure 15.24c). The polar iterated integral is
8/2
[[ f(r. 0 ) dA =
A =
6/4 Jr=√₂ csc 9
f(r, 0) r dr d0.
EXAMPLE 1 Find the limits of integration for integrating f(r, 8) over the region R
that lies inside the cardioid r = 1 + cos 0 and outside the circle r = 1.
Solution
1. We first sketch the region and label the bounding curves (Figure 15.25).
2. Next we find the r-limits of integration. A typical ray from the origin enters R where
r = 1 and leaves where r = 1 + cos 0.

Transcribed Image Text:Enters
at
r=1
r=1+cos 0
2
Enters at
7 = 0
Leaves at
r = 1 + cos
FIGURE 15.25 Finding the limits of
integration in polar coordinates for the
region in Example 1.
Area Differential in Polar Coordinates
dA = r dr do
Leaves at
r=V/4 cos 26
X
²-4 cos 20
FIGURE 15.26 To integrate over
the shaded region, we run from 0 to
√4 cos 20 and 6 from 0 to 7/4
(Example 2).
3. Finally we find the 0-limits of integration. The rays from the origin that intersect & run
from 0 = -7/2 to 0 = 7/2. The integral is
•/2 pl+c88
f(r, 0) r dr do.
If f(r, 0) is the constant function whose value is 1, then the integral of f over R is the
area of R.
Area in Polar Coordinates
The area of a closed and bounded region R in the polar coordinate plane is
15.4 Double Integrals in Polar Form 917
A = 4
- If
= 4
A =
This formula for area is consistent with all earlier formulas.
EXAMPLE 2
Find the area enclosed by the lemniscate 2² = 4 cos 20.
Solution We graph the lemniscate to determine the limits of integration (Figure 15.26) and
see from the symmetry of the region that the total area is 4 times the first-quadrant portion.
#/4 V4 cos 26
#/4
r=V/4 con 28
" r dr do = 4
-4.****
do
r dr do.
/4
2 cos 20 d0 - 4 sin 20
1/4
Jo
= 4.
Changing Cartesian Integrals into Polar Integrals
The procedure for changing a Cartesian integral f(x, y) dx dy into a polar integral has
two steps. First substitute x = r cos 8 and y = r sin 8, and replace dx dy by r dr do in the
Cartesian integral. Then supply polar limits of integration for the boundary of R. The Car-
tesian integral then becomes
Expert Solution

This question has been solved!
Explore an expertly crafted, step-by-step solution for a thorough understanding of key concepts.
This is a popular solution!
Trending now
This is a popular solution!
Step by step
Solved in 3 steps with 1 images

Similar questions
Recommended textbooks for you

Advanced Engineering Mathematics
Advanced Math
ISBN:
9780470458365
Author:
Erwin Kreyszig
Publisher:
Wiley, John & Sons, Incorporated

Numerical Methods for Engineers
Advanced Math
ISBN:
9780073397924
Author:
Steven C. Chapra Dr., Raymond P. Canale
Publisher:
McGraw-Hill Education

Introductory Mathematics for Engineering Applicat…
Advanced Math
ISBN:
9781118141809
Author:
Nathan Klingbeil
Publisher:
WILEY

Advanced Engineering Mathematics
Advanced Math
ISBN:
9780470458365
Author:
Erwin Kreyszig
Publisher:
Wiley, John & Sons, Incorporated

Numerical Methods for Engineers
Advanced Math
ISBN:
9780073397924
Author:
Steven C. Chapra Dr., Raymond P. Canale
Publisher:
McGraw-Hill Education

Introductory Mathematics for Engineering Applicat…
Advanced Math
ISBN:
9781118141809
Author:
Nathan Klingbeil
Publisher:
WILEY

Mathematics For Machine Technology
Advanced Math
ISBN:
9781337798310
Author:
Peterson, John.
Publisher:
Cengage Learning,

