The Region Bounded by the Curves

Oct 13, 2025 by wbrum.org 9 views

Introduction

In this article, we will explore the concept of finding the volume of a solid obtained by rotating a region about a line. This is a fundamental problem in calculus, and it has numerous applications in various fields such as physics, engineering, and economics. We will use the method of washers to find the volume of the solid obtained by rotating the region bounded by the curves $x=2-y^2$ and $x=y$ about the line $x=3$ .

The Method of Washers

The method of washers is a technique used to find the volume of a solid obtained by rotating a region about a line. It is based on the concept of the washer method, which states that the volume of a solid obtained by rotating a region about a line is equal to the area of the region multiplied by the distance between the line and the region.

The Region Bounded by the Curves

The region bounded by the curves $x=2-y^2$ and $x=y$ is a parabolic region. To find the volume of the solid obtained by rotating this region about the line $x=3$ , we need to find the area of the region and the distance between the line and the region.

Finding the Area of the Region

To find the area of the region, we need to find the intersection points of the curves. We can do this by setting the two equations equal to each other and solving for $y$ .

2-y^2=y

Solving for $y$ , we get:

y^2+y-2=0

Factoring the quadratic equation, we get:

(y-1)(y+2)=0

Solving for $y$ , we get:

y=1 \text{ or } y=-2

Now that we have the intersection points, we can find the area of the region. The area of the region is given by the integral:

A=\int_{-2}^{1} (2-y^2)-y \,dy

Evaluating the integral, we get:

A=\left[2y-\frac{y^3}{3}-\frac{y^2}{2}\right]_{-2}^{1}

Simplifying the expression, we get:

A=\frac{7}{6}

Finding the Distance Between the Line and the Region

The distance between the line $x=3$ and the region is given by the difference between the $x$ -coordinate of the line and the $x$ -coordinate of the region. Since the region is bounded by the curves $x=2-y^2$ and $x=y$ , the $x$ -coordinate of the region is given by the equation:

x=2-y^2

The distance between the line and the region is given by:

d=3-(2-y^2)

Simplifying the expression, we get:

d=y^2-1

Finding the Volume of the Solid

Now that we have the area of the region and the distance between the line and the region, we can find the volume of the solid obtained by rotating the region about the line $x=3$ . The volume of the solid is given by the integral:

V=\pi\int_{-2}^{1} (y^2-1)^2 \,dy

Evaluating the integral, we get:

V=\pi\left[\frac{y^5}{5}-\frac{y^3}{3}+y\right]_{-2}^{1}

Simplifying the expression, we get:

V=\frac{8\pi}{15}

Rounding to the Nearest Thousandth

To round the volume to the nearest thousandth, we need to multiply the volume by 1000 and round to the nearest integer.

V\approx\frac{8\pi}{15}\times1000\approx 2127.96

Rounding to the nearest thousandth, we get:

V\approx 2128

Conclusion

In this article, we used the method of washers to find the volume of the solid obtained by rotating the region bounded by the curves $x=2-y^2$ and $x=y$ about the line $x=3$ . We found the area of the region and the distance between the line and the region, and then used these values to find the volume of the solid. We rounded the volume to the nearest thousandth and obtained a final answer of 2128.

References

[1] "Calculus" by Michael Spivak
[2] "Calculus: Early Transcendentals" by James Stewart
[3] "Mathematics for the Nonmathematician" by Morris Kline

Glossary

Method of washers: A technique used to find the volume of a solid obtained by rotating a region about a line.
Washer method: A technique used to find the volume of a solid obtained by rotating a region about a line.
Region bounded by curves: A region bounded by two or more curves.
Distance between line and region: The distance between a line and a region.
Volume of solid: The volume of a solid obtained by rotating a region about a line.
Volume of a Solid Obtained by Rotating a Region About a Line: Q&A ====================================================================

Introduction

In our previous article, we explored the concept of finding the volume of a solid obtained by rotating a region about a line. We used the method of washers to find the volume of the solid obtained by rotating the region bounded by the curves $x=2-y^2$ and $x=y$ about the line $x=3$ . In this article, we will answer some of the most frequently asked questions about finding the volume of a solid obtained by rotating a region about a line.

Q: What is the method of washers?

A: The method of washers is a technique used to find the volume of a solid obtained by rotating a region about a line. It is based on the concept of the washer method, which states that the volume of a solid obtained by rotating a region about a line is equal to the area of the region multiplied by the distance between the line and the region.

Q: How do I find the area of the region?

A: To find the area of the region, you need to find the intersection points of the curves that bound the region. You can do this by setting the two equations equal to each other and solving for $y$ . Once you have the intersection points, you can find the area of the region by integrating the difference between the two curves with respect to $y$ .

Q: How do I find the distance between the line and the region?

A: The distance between the line and the region is given by the difference between the $x$ -coordinate of the line and the $x$ -coordinate of the region. You can find the $x$ -coordinate of the region by using the equation of the curve that bounds the region.

Q: What is the volume of a solid obtained by rotating a region about a line?

A: The volume of a solid obtained by rotating a region about a line is given by the integral of the area of the region multiplied by the distance between the line and the region with respect to $y$ .

Q: How do I round the volume to the nearest thousandth?

A: To round the volume to the nearest thousandth, you need to multiply the volume by 1000 and round to the nearest integer.

Q: What are some common applications of finding the volume of a solid obtained by rotating a region about a line?

A: Finding the volume of a solid obtained by rotating a region about a line has numerous applications in various fields such as physics, engineering, and economics. Some common applications include:

Calculating the volume of a tank or a container
Finding the volume of a solid obtained by rotating a region about a line in a three-dimensional space
Calculating the volume of a solid obtained by rotating a region about a line in a two-dimensional space

Q: What are some common mistakes to avoid when finding the volume of a solid obtained by rotating a region about a line?

A: Some common mistakes to avoid when finding the volume of a solid obtained by rotating a region about a line include:

Failing to find the intersection points of the curves that bound the region
Failing to find the area of the region
Failing to find the distance between the line and the region
Failing to round the volume to the nearest thousandth

Conclusion

In this article, we answered some of the most frequently asked questions about finding the volume of a solid obtained by rotating a region about a line. We hope that this article has been helpful in clarifying some of the concepts and techniques involved in finding the volume of a solid obtained by rotating a region about a line.

References

[1] "Calculus" by Michael Spivak
[2] "Calculus: Early Transcendentals" by James Stewart
[3] "Mathematics for the Nonmathematician" by Morris Kline

Glossary

Method of washers: A technique used to find the volume of a solid obtained by rotating a region about a line.
Washer method: A technique used to find the volume of a solid obtained by rotating a region about a line.
Region bounded by curves: A region bounded by two or more curves.
Distance between line and region: The distance between a line and a region.
Volume of solid: The volume of a solid obtained by rotating a region about a line.