# disc method

Find the volume of the solid that is generated by rotating around the indicated axis the plane region bounded by the fiven curves.

1) y=√x,y=0,x=4; The x-axis

2) y= 1/x, y=0, x=0.1,x=1; the x-axis

3)Find the volume of the ellipsoid generated by rotating around the x-axis the region bounded by the ellipse with equation.

(x/a)^2 + (y/b)^2 =1

4) (a) Find the volume of the unbounded solid generated by rotating the unbounded region around the x-axis. This is the region between the graph of y=e^-x and the x-axis for x >1. (Compute the volume from x=1 to x=b, where b>1. Then find the limit of this volume as b->+∞).

(b) What happens if y= 1/√x instead?

https://brainmass.com/math/integrals/volume-solid-ellipsoid-unbounded-solid-268199

#### Solution Preview

(1) By the disc method we get

pi. int._{0 to 4} (sqrt(x))^2 dx = 8 .pi

Using cylindrical shells we get

2.pi int_{0 to 2} y (4 - y^2) dy = 2.pi (8 - 4) = 8.pi

(2) the ...

#### Solution Summary

The volume of solids and ellipsoid for an unbounded solid are determined.