Posted by **Ashley** on Thursday, December 15, 2011 at 7:15pm.

find the volume of the solid obtained by rotating the region bounded by the given curves about the specified axis y=x^2+1; y=9-x^2; about y=-1

- Calc -
**MathMate**, Thursday, December 15, 2011 at 9:03pm
First find the intersections between the two curves, they are the limits of integration. They can be found readily as x=±2.

Next, we check that the curves do not cross the axis y=-1 between the limits of integration. Otherwise the limits of integration must change.

Now use the washer method to calculate the area, since the "outer" radius R is based on the upper curve, and the inner radius r is on the lower curve.

The integration formula is then

Area = π∫(R(x)^2-r(x)^2)dx

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