The region of the curve bounded by x = 1 and x = 2 and y = 0, is rotated about the y axis. Find the volume of the solid.

i drew the diagram and it doesn't look doable. Would I have to consider volumes by slicing?

thanks

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- Apr 27th 2010, 03:57 AMdifferentiatevolumes rotate about y axis
The region of the curve bounded by x = 1 and x = 2 and y = 0, is rotated about the y axis. Find the volume of the solid.

i drew the diagram and it doesn't look doable. Would I have to consider volumes by slicing?

thanks - Apr 27th 2010, 07:54 AMHallsofIvy
It certainly

**is**"doable". The region in the xy-plane is a "quadrilateral with one curved side, vertices at (1, 0), (2, 0), and (1, e). There would be a problem with doing it as "washers" since there would be a change of formula at (1, e).

If you "slice" it parallel to the y-axis, rotating around the y-axis, each "slice" would be a cylinder, of thickness dx, and height the distance from y= 0 to which is .

Since this is rotated around the x-axis, the radius of each cylinder is x and the area is . The volume of each thin cylinder is and the entire volume is given by the integral

.