By changing to polar coordinates, evaluate the integral where D is the disk x² + y² ≤ 36. Answer= (x +ỷ)52 dxdy

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Problem Statement:**

By changing to polar coordinates, evaluate the integral

\[
\iint_D (x^2 + y^2)^{5/2} \, dx \, dy
\]

where \( D \) is the disk \( x^2 + y^2 \leq 36 \).

**Solution:**

*Note: To solve this problem, convert the given integral from Cartesian coordinates to polar coordinates.*

**Explanation:**

- The disk \( x^2 + y^2 \leq 36 \) represents a circle with a radius of 6 centered at the origin.
- In polar coordinates, \( x^2 + y^2 = r^2 \) and \( dx \, dy = r \, dr \, d\theta \).

**Convert the Integral:**

The integral becomes:

\[
\int_0^{2\pi} \int_0^6 (r^2)^{5/2} \cdot r \, dr \, d\theta
\]

Simplify the expression:

\[
\int_0^{2\pi} \int_0^6 r^6 \, dr \, d\theta
\]

Now, evaluate the integral in the order of \( dr \) and \( d\theta \):

1. Integrate with respect to \( r \):

\[
\int_0^6 r^6 \, dr = \left[ \frac{r^7}{7} \right]_0^6 = \frac{6^7}{7}
\]

2. Integrate with respect to \( \theta \):

\[
\int_0^{2\pi} \frac{6^7}{7} \, d\theta = \frac{6^7}{7} \cdot \theta \bigg]_0^{2\pi} = \frac{6^7}{7} \cdot 2\pi
\]

3. Compute the final answer:

\[
\frac{6^7 \cdot 2\pi}{7}
\]

Thus, the evaluated integral is:

**Answer =** \(\frac{6^7 \cdot 2\pi}{7}\)
Transcribed Image Text:**Problem Statement:** By changing to polar coordinates, evaluate the integral \[ \iint_D (x^2 + y^2)^{5/2} \, dx \, dy \] where \( D \) is the disk \( x^2 + y^2 \leq 36 \). **Solution:** *Note: To solve this problem, convert the given integral from Cartesian coordinates to polar coordinates.* **Explanation:** - The disk \( x^2 + y^2 \leq 36 \) represents a circle with a radius of 6 centered at the origin. - In polar coordinates, \( x^2 + y^2 = r^2 \) and \( dx \, dy = r \, dr \, d\theta \). **Convert the Integral:** The integral becomes: \[ \int_0^{2\pi} \int_0^6 (r^2)^{5/2} \cdot r \, dr \, d\theta \] Simplify the expression: \[ \int_0^{2\pi} \int_0^6 r^6 \, dr \, d\theta \] Now, evaluate the integral in the order of \( dr \) and \( d\theta \): 1. Integrate with respect to \( r \): \[ \int_0^6 r^6 \, dr = \left[ \frac{r^7}{7} \right]_0^6 = \frac{6^7}{7} \] 2. Integrate with respect to \( \theta \): \[ \int_0^{2\pi} \frac{6^7}{7} \, d\theta = \frac{6^7}{7} \cdot \theta \bigg]_0^{2\pi} = \frac{6^7}{7} \cdot 2\pi \] 3. Compute the final answer: \[ \frac{6^7 \cdot 2\pi}{7} \] Thus, the evaluated integral is: **Answer =** \(\frac{6^7 \cdot 2\pi}{7}\)
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