Math Problem Statement

Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified axis. y=x^6, y =1 about y=5.

Solution

We are tasked with finding the volume of the solid obtained by rotating the region bounded by y=x6y = x^6 and y=1y = 1 about the axis y=5y = 5. To solve this, we will use the method of cylindrical shells.

Step-by-step solution:

  1. Sketch the region: The region is bounded by the curve y=x6y = x^6, the horizontal line y=1y = 1, and we are rotating around y=5y = 5, which is a horizontal axis above the region.

  2. Set up the cylindrical shells: The formula for the volume using cylindrical shells is:

    V=2πab(rshell)(hshell)dxV = 2\pi \int_a^b (r_{\text{shell}})(h_{\text{shell}}) \, dx

    Here:

    • rshellr_{\text{shell}} is the distance from the shell to the axis of rotation y=5y = 5, which is rshell=5yr_{\text{shell}} = 5 - y.
    • hshellh_{\text{shell}} is the height of the shell, which is determined by the curve equation y=x6y = x^6.
  3. Express the radius and height:

    • The radius from y=5y = 5 to a point on the curve is rshell=5y=5x6r_{\text{shell}} = 5 - y = 5 - x^6.
    • The height of the shell is the difference between the upper boundary y=1y = 1 and the curve y=x6y = x^6. Therefore, hshell=1x6h_{\text{shell}} = 1 - x^6.
  4. Determine the limits of integration: The curves intersect at y=1y = 1 and y=x6y = x^6. Solving x6=1x^6 = 1, we find that the limits of integration are from x=0x = 0 to x=1x = 1.

  5. Set up the integral: The volume integral becomes:

    V=2π01(5x6)(1x6)dxV = 2\pi \int_0^1 (5 - x^6)(1 - x^6) \, dx

  6. Expand the integrand: (5x6)(1x6)=5(1x6)x6(1x6)(5 - x^6)(1 - x^6) = 5(1 - x^6) - x^6(1 - x^6) Simplifying: =55x6x6+x12= 5 - 5x^6 - x^6 + x^{12} =56x6+x12= 5 - 6x^6 + x^{12}

  7. Evaluate the integral: Now, integrate term by term: V=2π01(56x6+x12)dxV = 2\pi \int_0^1 \left( 5 - 6x^6 + x^{12} \right) \, dx =2π[5x6x77+x1313]01= 2\pi \left[ 5x - \frac{6x^7}{7} + \frac{x^{13}}{13} \right]_0^1 Substituting the limits: V=2π(567+113)V = 2\pi \left( 5 - \frac{6}{7} + \frac{1}{13} \right) V=2π(567+113)V = 2\pi \left( 5 - \frac{6}{7} + \frac{1}{13} \right)

    To simplify the expression inside the parentheses, find a common denominator: V=2π(455917891+791)V = 2\pi \left( \frac{455}{91} - \frac{78}{91} + \frac{7}{91} \right) V=2π(45578+791)V = 2\pi \left( \frac{455 - 78 + 7}{91} \right) V=2π(38491)V = 2\pi \left( \frac{384}{91} \right)

    Therefore, the volume is: V=768π91V = \frac{768\pi}{91}

Final Answer:

The volume of the solid is 768π91\frac{768\pi}{91} cubic units.

Would you like further details or have any questions?

Here are five related questions to explore:

  1. How would the volume change if the axis of rotation was y=3y = 3 instead of y=5y = 5?
  2. Can you find the volume if we rotate the same region about the x-axis?
  3. What is the volume of the solid if we rotate the region around the line x=1x = 1?
  4. How does the method of disks or washers compare to the method of cylindrical shells for this problem?
  5. What if the region is rotated around the line y=1y = -1? How would the integral change?

Tip: The method of cylindrical shells is often simpler when rotating around a horizontal or vertical line that is not an axis.

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Math Problem Analysis

Mathematical Concepts

Calculus
Volumes of Solids of Revolution
Cylindrical Shell Method
Integration

Formulas

V = 2π ∫(a to b) (r_shell)(h_shell) dx

Theorems

Method of Cylindrical Shells
Definite Integral

Suitable Grade Level

Grades 11-12 or Calculus I