Math Problem Statement

Find the volume V of the solid obtained by rotating the region bounded by the given curves about the specified line. y = 5/x , x = 6, x = 12, y = 0; about the x-axis

Solution

To find the volume VV of the solid obtained by rotating the region bounded by the curves y=5xy = \frac{5}{x}, x=6x = 6, x=12x = 12, and y=0y = 0 about the x-axis, we can use the method of disk integration.

Step 1: Set Up the Integral

The formula for the volume VV when rotating a region around the x-axis is given by: V=πab(f(x))2dxV = \pi \int_{a}^{b} \left( f(x) \right)^2 \, dx where f(x)f(x) represents the function y=5xy = \frac{5}{x}, and aa and bb are the bounds of integration, which are x=6x = 6 and x=12x = 12, respectively.

Step 2: Substitute the Function and Bounds

V=π612(5x)2dxV = \pi \int_{6}^{12} \left( \frac{5}{x} \right)^2 \, dx

Step 3: Simplify the Integral

V=π61225x2dxV = \pi \int_{6}^{12} \frac{25}{x^2} \, dx

Step 4: Integrate

To integrate 25x2\frac{25}{x^2}, recall that the integral of x2x^{-2} is x1-x^{-1}, or 1x-\frac{1}{x}. Therefore: 25x2dx=25x\int \frac{25}{x^2} \, dx = -\frac{25}{x}

Now, apply the limits from 6 to 12: V=π[25x]612V = \pi \left[ -\frac{25}{x} \right]_{6}^{12}

Step 5: Evaluate the Definite Integral

V=π(2512+256)V = \pi \left( -\frac{25}{12} + \frac{25}{6} \right)

Simplifying: V=π(2562512)V = \pi \left( \frac{25}{6} - \frac{25}{12} \right)

Find a common denominator: V=π(50122512)=π2512V = \pi \left( \frac{50}{12} - \frac{25}{12} \right) = \pi \cdot \frac{25}{12}

Therefore: V=25π12V = \frac{25\pi}{12}

Final Answer

The volume VV of the solid is: V=25π12cubic unitsV = \frac{25\pi}{12} \, \text{cubic units}

Would you like more details or have any questions?

Here are some related questions to explore further:

  1. How would the volume change if the rotation were around the y-axis instead?
  2. What would the volume be if the region were bounded by y=10xy = \frac{10}{x} instead of y=5xy = \frac{5}{x}?
  3. How does the method of shells differ from the disk method in this context?
  4. What is the geometric interpretation of the volume of revolution?
  5. Can you find the surface area of the solid obtained by rotating the same region?

Tip: When using integration methods for volumes of revolution, carefully choosing the method (disks, washers, or shells) that matches the problem's symmetry can simplify the computation.

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Math Problem Analysis

Mathematical Concepts

Calculus
Volumes of Revolution
Integral Calculus

Formulas

Volume of revolution using disk method

Theorems

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Suitable Grade Level

Advanced High School