Math Problem Statement

Let R be the region bounded by the following curves. Use the shell method to find the volume of the solid generated when R is revolved about the​ y-axis.

y equals 8 left parenthesis 1 plus 8 x squared right parenthesis Superscript negative 1y=81+8x2−1​,

yequals=​0,

xequals=​0,

and

xequals=2

20xy

y equals StartFraction 8 Over 1 plus 8 x squared EndFractiony=81+8x2

Upper RR

A coordinate system has a horizontal x-axis labeled from 0 to 2 plus and an unlabeled positive vertical y-axis. From left to right, a curve labeled y equals StartFraction 8 Over 1 plus 8 x squared EndFraction starts on the positive y-axis and falls at an increasing and then decreasing rate in quadrant 1. As x approaches positive infinity, the curve approaches the x-axis from above. A dashed vertical line segment extends from the x-axis at 2 to the curve. The region above the x-axis, to the right of the y-axis, below the curve, and to the left of the vertical line segment is shaded and labeled R.

Question content area bottom

Part 1

Set up the integral that gives the volume of the solid using the shell method. Use increasing limits of integration. Select the correct choice below and fill in the answer boxes to complete your choice.

​(Type exact​ answers.)

Solution

To find the volume of the solid generated by revolving the region RR around the yy-axis using the shell method, we follow the general formula for the shell method:

V=2πab(radius)×(height)dxV = 2\pi \int_{a}^{b} \text{(radius)} \times \text{(height)} \, dx

Given curves:

  • y=81+8x2y = \frac{8}{1 + 8x^2}
  • y=0y = 0
  • x=0x = 0
  • x=2x = 2

We revolve this region around the yy-axis, so:

  • The radius of each cylindrical shell is simply xx.
  • The height of each shell is the function y=81+8x2y = \frac{8}{1 + 8x^2}.

The limits of integration for xx are from 0 to 2.

Thus, the volume VV is given by:

V=2π02x81+8x2dxV = 2\pi \int_0^2 x \cdot \frac{8}{1 + 8x^2} \, dx

This is the setup for the integral. Would you like me to solve the integral for the volume?


5 Related Questions:

  1. What is the geometric interpretation of the shell method in calculating volume?
  2. How does the shell method differ from the disk/washer method?
  3. Can the volume also be calculated using the disk method for this problem? If so, how?
  4. What happens if we revolve the region around the xx-axis instead?
  5. What are the limits of integration if we were to revolve the region around a vertical line other than the yy-axis?

Tip:

When using the shell method, the "radius" is always the distance from the axis of revolution to the point on the curve, and the "height" is the value of the function itself.

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Math Problem Analysis

Mathematical Concepts

Calculus
Volume of Solids of Revolution
Shell Method
Definite Integrals

Formulas

V = 2π ∫[a, b] (radius) × (height) dx
y = 8 / (1 + 8x^2)

Theorems

Shell Method for Volume Calculation

Suitable Grade Level

Grades 11-12 (AP Calculus), College Calculus