Use the method of cylindrical shells to find the volume V generated by rotating the region bounded by the given curves about the specified axis.x = 7y2, y ≥ 0, x = 7; about y = 2
Question
Use the method of cylindrical shells to find the volume V generated by rotating the region bounded by the given curves about the specified axis.x = 7y2, y ≥ 0, x = 7; about y = 2
Solution
The method of cylindrical shells is a method for finding the volume of a solid of revolution. The basic idea is to approximate the region by cylinders and then to take the limit as the number of cylinders goes to infinity.
Here are the steps to solve the problem:
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Identify the region: The region is bounded by the curves x = 7y^2, y ≥ 0, and x = 7.
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Set up the integral: The volume V of the solid of revolution is given by the integral ∫[a,b] 2πrh dx, where r is the radius of the cylindrical shell and h is the height of the cylindrical shell. In this case, the radius r is |y - 2| and the height h is |7 - 7y^2|. The limits of integration are from y = 0 to y = sqrt(1).
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Evaluate the integral:
V = ∫[0,sqrt(1)] 2π|y - 2||7 - 7y^2| dy = 2π ∫[0,sqrt(1)] |y - 2||7(1 - y^2)| dy = 2π ∫[0,sqrt(1)] (2 - y)(7 - 7y^2) dy = 2π [7y - (7/3)y^3 - 2y + (2/3)y^3] evaluated from 0 to sqrt(1) = 2π [7sqrt(1) - (7/3)(1) - 2sqrt(1) + (2/3)(1)] = 2π [5sqrt(1) - (5/3)] = 2π [(5/3)sqrt(1)] = (10/3)π sqrt(1) = (10/3)π.
So, the volume V of the solid generated by rotating the region bounded by the given curves about the line y = 2 is (10/3)π cubic units.
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This question has several parts that must be completed sequentially. If you skip a part of the question, you will not receive any points for the skipped part, and you will not be able to come back to the skipped part.Tutorial ExerciseUse 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.Step 1Rotating a vertical strip around the y-axis creates a cylinder with radius r = $$x and height h = $$4e−x2 . Sketch the region and a typical shell. Step 2Now we can say that the volume of the solid created by rotating the region under y = 4e−x2and above the x-axis between x = 0 and x = 1 around the y-axis isV = b2𝜋rh dxa= 2𝜋x dx.0
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