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I have a question concerning solid of revolution.

The bowl-shaped volume formed by rotating the area circumscribed between y=bcosh(1) and y=bcosh(x/a) around the y axis was given to us by the instructor as pi*b*int [x^2*d(cosh(x/a))] between 0 and a.

My question is why are the integration boundaries not -a and a, but 0 and a, OR, alternatively, why wasn't the final answer then multiplied by 2?

When the same area is rotated around the x axis the integration boundaries are indeed -a and a. Why aren't the boundaries similar in both cases?

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# Solid of revolution.

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