Volume of Revolved Area: Washer Method Problem 1 | x=y^2, x=4, y=2

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In summary, the volume generated by revolving the area bounded by x=y^2 and x=4 about the line y=2 is given by the integral \pi\int(4-(2+\sqrt{x})^2)dx from 0 to 4, where the outer radius is 2+sqrt(x) and the inner radius is 2-sqrt(x). The boundaries of the region are given by y=sqrt(x) and y=-sqrt(x).
  • #1
elitespart
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1. Find the volume generated by revolving the area bounded by x=y[tex]^{2}[/tex] and x=4 about the line y=2.


Is it [tex]\pi\int(4-(2-\sqrt{x})^{2}dx[/tex] from 0 to 4?
 
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  • #2
No. The inner radius is (2-sqrt(x)). What's the outer radius? It doesn't lie on the x-axis.
 
  • #3
Dick said:
Yes, if you fix the unmatched parenthesis which makes it look a little confusing. The outer radius of the washer is 2 and the inner radius is (2-sqrt(x)).

oh whoops forgot to add a bracket at the end. Thanks for your help.
 
  • #4
elitespart said:
oh whoops forgot to add a bracket at the end. Thanks for your help.

Hold it. I gave it a second thought and edited my answer. The area enclosed by x=4 and y^2=x has pieces both about and below the x-axis.
 
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  • #5
So it's 4 instead of 2?
 
  • #6
No, y^2=x gives y=sqrt(x) or y=-sqrt(x). Those are the boundaries of the region. Your original answer would be ok if they had specified y=0 as a boundary. But they didn't.
 
  • #7
Dick said:
No, y^2=x gives y=sqrt(x) or y=-sqrt(x). Those are the boundaries of the region. Your original answer would be ok if they had specified y=0 as a boundary. But they didn't.

oh okay. So would y=2 factor into the outer radius too? Meaning r = [2 - (-sqrt(x))]?
 
  • #8
elitespart said:
oh okay. So would y=2 factor into the outer radius too? Meaning r = [2 - (-sqrt(x))]?

Exactly. The outer radius is 2+sqrt(x).
 
  • #9
awesome. Thanks again.
 

1. What is the Washer Method problem?

The Washer Method problem is a mathematical concept used in calculus to find the volume of an irregularly shaped solid formed by rotating a curve around an axis.

2. How does the Washer Method work?

The Washer Method involves finding the volume of a solid by taking the integral of the area of a cross section of the solid, which is then multiplied by the thickness of the solid and integrated over the given interval.

3. What is the difference between the Washer Method and the Shell Method?

The Washer Method and the Shell Method both involve finding the volume of a solid of revolution, but they use different techniques. The Washer Method involves slicing the solid into cross sections perpendicular to the axis of rotation, while the Shell Method involves slicing the solid into cylindrical shells parallel to the axis of rotation.

4. What are the common mistakes made when using the Washer Method?

Common mistakes when using the Washer Method include using the wrong formula, not properly setting up the integral, and not correctly identifying the limits of integration.

5. How can I improve my understanding and skills in solving Washer Method problems?

To improve your understanding and skills in solving Washer Method problems, it is important to practice using the method with various types of curves, pay attention to the setup of the integral, and seek help from a tutor or teacher if needed.

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