Math Problem Statement

lets find the volume of a solid revolving about line x=1. IT is bounded by curves y=x^2+1, x=0, x=1, y=0

Solution

To find the volume of the solid formed by revolving the region bounded by the curves y=x2+1y = x^2 + 1, x=0x = 0, x=1x = 1, and y=0y = 0 about the line x=1x = 1, we can use the method of cylindrical shells. This method is particularly useful when revolving a region around a vertical line that is not one of the axes.

Step-by-Step Solution:

  1. Region Boundaries:

    • y=x2+1y = x^2 + 1 (upper boundary)
    • y=0y = 0 (lower boundary)
    • x=0x = 0 (left boundary)
    • x=1x = 1 (right boundary)
  2. Cylindrical Shells Method: When rotating about the vertical line x=1x = 1, the formula for the volume of a cylindrical shell is:

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

    • Radius: The distance from the line of revolution x=1x = 1 to a point xx is 1x=1x|1 - x| = 1 - x.
    • Height: The height of the shell is the function y=x2+1y = x^2 + 1.

    So, the volume integral becomes: V=2π01(1x)(x2+1)dxV = 2\pi \int_{0}^{1} (1 - x)(x^2 + 1) \, dx

  3. Expand the integrand: (1x)(x2+1)=(1x2)+(11)(xx2)(x1)(1 - x)(x^2 + 1) = (1 \cdot x^2) + (1 \cdot 1) - (x \cdot x^2) - (x \cdot 1) Simplifying: =x2+1x3x= x^2 + 1 - x^3 - x

    Thus, the integral becomes: V=2π01(x2+1x3x)dxV = 2\pi \int_{0}^{1} (x^2 + 1 - x^3 - x) \, dx

  4. Integrate each term: (x2+1x3x)dx=[x33+xx44x22]01\int (x^2 + 1 - x^3 - x) \, dx = \left[\frac{x^3}{3} + x - \frac{x^4}{4} - \frac{x^2}{2}\right]_{0}^{1}

  5. Evaluate the integral at the bounds 00 and 11:

    • At x=1x = 1: 133+1144122=13+11412\frac{1^3}{3} + 1 - \frac{1^4}{4} - \frac{1^2}{2} = \frac{1}{3} + 1 - \frac{1}{4} - \frac{1}{2} Combine the fractions: =13+11412=412+1212312612= \frac{1}{3} + 1 - \frac{1}{4} - \frac{1}{2} = \frac{4}{12} + \frac{12}{12} - \frac{3}{12} - \frac{6}{12} Simplifying: =4+123612=712= \frac{4 + 12 - 3 - 6}{12} = \frac{7}{12}

    • At x=0x = 0, all terms are 0.

  6. Multiply by 2π2\pi: V=2π×712=7π6V = 2\pi \times \frac{7}{12} = \frac{7\pi}{6}

Final Answer:

The volume of the solid is 7π6\frac{7\pi}{6}.


Would you like more details or have any further questions? Here are some related problems for you to explore:

  1. Find the volume if the region is revolved around the line x=2x = 2.
  2. What is the volume when the same region is revolved around the y-axis?
  3. Find the centroid of the region before revolving.
  4. Use the disk method to compute the volume revolving around the x-axis.
  5. How does the volume change if the upper boundary is y=2x2+1y = 2x^2 + 1?

Tip: The method of cylindrical shells is generally easier for problems involving revolutions around vertical lines.

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Math Problem Analysis

Mathematical Concepts

Volume of Solids
Cylindrical Shells Method
Integration

Formulas

V = 2π ∫ (radius)(height) dx
Radius: 1 - x
Height: y = x^2 + 1

Theorems

Cylindrical Shells Method for Volume

Suitable Grade Level

College Level Calculus