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Use the method of cylindrical shells to find the volume V generated by rotating the region bounded by the given curves about the y-axis.y = 4e−x2,      y = 0,      x = 0,      x = 1Sketch the region and a typical shell.

Question

Use the method of cylindrical shells to find the volume V generated by rotating the region bounded by the given curves about the y-axis.y = 4e−x2,      y = 0,      x = 0,      x = 1Sketch the region and a typical shell.

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Solution

The method of cylindrical shells is a method for finding the volume of a solid of revolution. The idea is to approximate the volume by a union of thin cylindrical shells, and then to take the limit as the thickness of the shells goes to zero.

Here are the steps to solve the problem:

  1. Sketch the region: The region is bounded by the curve y = 4e^(-x^2), the x-axis (y = 0), the y-axis (x = 0), and the line x = 1. It's a curve that starts at the point (0,4) on the y-axis, decreases as x increases, and reaches the x-axis at x = 1.

  2. Identify a typical shell: A typical shell is a thin vertical strip in the region, with thickness dx, height y, and radius x (since we're rotating about the y-axis). The volume of this shell is approximately 2πxy*dx.

  3. Set up the integral: To find the total volume, we integrate the volume of a typical shell from x = 0 to x = 1. This gives us the integral ∫ from 0 to 1 of 2πx4e^(-x^2) dx.

  4. Evaluate the integral: This is an integral that can be solved by substitution. Let u = -x^2, so du = -2x dx. The integral becomes -2π ∫ from 0 to -1 of 4e^u du, which is -8π [e^u] from 0 to -1. Evaluating this gives -8π(e^(-1) - e^0) = -8π(1/e - 1) = 8π(1 - 1/e).

So the volume V generated by rotating the region about the y-axis is 8π(1 - 1/e) cubic units.

This problem has been solved

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