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, y = sqrtx; about x = 2

Solution

To find the volume VV of the solid obtained by rotating the region bounded by the curves y=xy = x and y=xy = \sqrt{x} about the line x=2x = 2, we can use the method of cylindrical shells.

Step-by-Step Solution:

  1. Identify the region and the curves:

    • The curves are y=xy = x and y=xy = \sqrt{x}.
    • The region is bounded by these curves.
  2. Find the intersection points:

    • Set y=xy = x equal to y=xy = \sqrt{x} to find the intersection points: x=xx = \sqrt{x} Squaring both sides: x2=xx^2 = x Rearrange to: x2x=0x^2 - x = 0 Factor: x(x1)=0x(x - 1) = 0 So, x=0x = 0 and x=1x = 1.

      The region of integration is from x=0x = 0 to x=1x = 1.

  3. Set up the volume integral using the method of 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, the radius of the shell is the distance from the curve to the line x=2x = 2: rshell=2xr_{\text{shell}} = 2 - x
    • The height of the shell is the difference between the upper and lower curves: hshell=xxh_{\text{shell}} = \sqrt{x} - x

    Therefore, the integral becomes: V=2π01(2x)(xx)dxV = 2\pi \int_{0}^{1} (2 - x)(\sqrt{x} - x) \, dx

  4. Expand and simplify the integrand: V=2π01[(2x)x(2x)x]dxV = 2\pi \int_{0}^{1} \left[(2 - x)\sqrt{x} - (2 - x)x\right] \, dx Distribute the terms: V=2π01[2xxx2x+x2]dxV = 2\pi \int_{0}^{1} \left[2\sqrt{x} - x\sqrt{x} - 2x + x^2\right] \, dx

  5. Integrate term by term:

    • For 2x2\sqrt{x}, use xdx=23x3/2\int \sqrt{x} \, dx = \frac{2}{3}x^{3/2}: 2xdx=43x3/22\int \sqrt{x} \, dx = \frac{4}{3}x^{3/2}
    • For xx-x\sqrt{x}, use x3/2dx=25x5/2\int x^{3/2} \, dx = \frac{2}{5}x^{5/2}: xxdx=25x5/2-\int x\sqrt{x} \, dx = -\frac{2}{5}x^{5/2}
    • For 2x-2x, use xdx=12x2\int x \, dx = \frac{1}{2}x^2: 2xdx=x2-2\int x \, dx = -x^2
    • For x2x^2, use x2dx=13x3\int x^2 \, dx = \frac{1}{3}x^3: x2dx=13x3\int x^2 \, dx = \frac{1}{3}x^3
  6. Evaluate the definite integral: V=2π[(43x3/225x5/2x2+13x3)01]V = 2\pi \left[\left(\frac{4}{3}x^{3/2} - \frac{2}{5}x^{5/2} - x^2 + \frac{1}{3}x^3\right)\bigg|_{0}^{1}\right] At x=1x = 1: 43(1)25(1)(1)+13(1)=43251+13\frac{4}{3}(1) - \frac{2}{5}(1) - (1) + \frac{1}{3}(1) = \frac{4}{3} - \frac{2}{5} - 1 + \frac{1}{3} At x=0x = 0, the integral evaluates to 0.

    Therefore: V=2π(43+13125)=2π(5325)=2π(2515615)=2π(1915)V = 2\pi \left(\frac{4}{3} + \frac{1}{3} - 1 - \frac{2}{5}\right) = 2\pi \left(\frac{5}{3} - \frac{2}{5}\right) = 2\pi \left(\frac{25}{15} - \frac{6}{15}\right) = 2\pi \left(\frac{19}{15}\right) V=38π15V = \frac{38\pi}{15}

Final Answer:

The volume VV of the solid is 38π15\boxed{\frac{38\pi}{15}} cubic units.

Would you like further details on any of the steps? Here are five related questions:

  1. How do you set up the volume integral using the washer method for this problem?
  2. What is the difference between the method of cylindrical shells and the disk/washer method?
  3. How do you visualize the solid formed by rotating the region around the line x=2x = 2?
  4. Can we use a different axis of rotation and how does that affect the integral setup?
  5. How would the problem change if the region was rotated around the y-axis instead?

Tip: When rotating around vertical lines (not the y-axis), the method of cylindrical shells is often more convenient than the disk/washer method.

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Math Problem Analysis

Mathematical Concepts

Integration
Volumes of Revolution
Cylindrical Shells

Formulas

Volume using cylindrical shells: V = 2\pi \int_{a}^{b} (r_{\text{shell}})(h_{\text{shell}}) \, dx

Theorems

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Suitable Grade Level

Advanced Mathematics