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I need to find the volume of the solid that is formed when the (x>0, y< -1) region of the curve y= -1/x is rotated about the y-axis.

If I'm correct, this volume can be calculated by: Evaluating the definite integral (upper bound = -1, lower bound = -infinity) of π*(1/y²) with respect to y.

In evaluating this integral, I got up to: Volume = (-π/1) - (-π/infinity) = -π

But how can a volume be a negative value? Please let me know if I've done anything wrong, and explain how to get the correct answer if you can.

Thank you x

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(-1/y²) should instead be (-1/y)². That should fix it.

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  • $\begingroup$ Thank you! So is the correct answer Volume = π units^3 ? $\endgroup$ – Tom Symonds Feb 7 '16 at 1:31
  • $\begingroup$ Yes. Good work! If you are new to MSE read through the tutorial. You should up vote and/or accept this answer if you consider it complete. $\endgroup$ – John Molokach Feb 7 '16 at 1:41

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