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 =

x − 1 , y = 0, x = 5; about the x-axis V =

Incorrect: Your answer is incorrect.

Solution

To find the volume VV of the solid obtained by rotating the region bounded by the given curves about the x-axis, we use the disk method. The curves provided are:

y=x1,y=0,andx=5y = x - 1, \quad y = 0, \quad \text{and} \quad x = 5

Step 1: Determine the bounds of integration

The region is bounded horizontally by y=0y = 0 (the x-axis) and y=x1y = x - 1, and vertically by x=1x = 1 (where y=0y = 0) and x=5x = 5.

Step 2: Set up the disk method integral

When rotating around the x-axis, the volume is given by:

V=πab[f(x)]2dxV = \pi \int_{a}^{b} [f(x)]^2 \, dx

Here, f(x)=x1f(x) = x - 1, and the limits of integration are from x=1x = 1 to x=5x = 5.

Step 3: Write the integral

V=π15(x1)2dxV = \pi \int_{1}^{5} (x - 1)^2 \, dx

Step 4: Expand the integrand

(x1)2=x22x+1(x - 1)^2 = x^2 - 2x + 1

Step 5: Integrate

Now, integrate term by term: V=π15(x22x+1)dxV = \pi \int_{1}^{5} (x^2 - 2x + 1) \, dx

V=π[x33x2+x]15V = \pi \left[ \frac{x^3}{3} - x^2 + x \right]_{1}^{5}

Step 6: Evaluate the integral at the bounds

Evaluate at x=5x = 5: (53352+5)=(125325+5)=125320\left( \frac{5^3}{3} - 5^2 + 5 \right) = \left( \frac{125}{3} - 25 + 5 \right) = \frac{125}{3} - 20

Evaluate at x=1x = 1: (13312+1)=(131+1)=13\left( \frac{1^3}{3} - 1^2 + 1 \right) = \left( \frac{1}{3} - 1 + 1 \right) = \frac{1}{3}

Now, subtract the two values: V=π[(125320)13]=π(125360313)=π(1256013)=π(643)V = \pi \left[ \left( \frac{125}{3} - 20 \right) - \frac{1}{3} \right] = \pi \left( \frac{125}{3} - \frac{60}{3} - \frac{1}{3} \right) = \pi \left( \frac{125 - 60 - 1}{3} \right) = \pi \left( \frac{64}{3} \right)

Final Answer

V=64π3 cubic unitsV = \frac{64\pi}{3} \text{ cubic units}

This is the correct volume of the solid.

Do you need further details or have any questions?

Here are 5 related questions for you:

  1. How would the integral change if the region was rotated about the y-axis instead?
  2. What if the curve was rotated around the line y=2y = 2? How would that affect the volume?
  3. Can you find the volume if the region was between x=2x = 2 and x=5x = 5?
  4. How does the method change if the curves were more complex, such as a quadratic function?
  5. What if the problem involved finding the surface area instead of volume?

Tip: For rotating a region around a horizontal or vertical line other than the axes, always adjust the radius to account for the distance from the axis of rotation.

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Math Problem Analysis

Mathematical Concepts

Volume of solids of revolution
Disk method integration
Rotation about the x-axis

Formulas

Volume using disk method: V = \pi \int_{a}^{b} [f(x)]^2 \, dx

Theorems

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Suitable Grade Level

Advanced High School