# Thread: Volumes Of Revolution (Tricky Set-up)

1. ## Volumes Of Revolution (Tricky Set-up)

Calculate the volume of the solid obtained by rotating the region between the graphs of y = 1/(x^2 - 3x + 2) and y = 0 for 4 ≤ x ≤ 10 around the y-axis.

I can't seem to set this up. It's being rotated about the y-axis so the function should be in terms of y, but getting it be in terms of y is impossible.

What should I do?

2. ## Re: Volumes Of Revolution (Tricky Set-up)

Have you heard of discs vs. cylinders?

Originally Posted by bhaktir
It's being rotated about the y-axis so the function should be in terms of y
... Only if you are confined to discs (or 'washers')... where you rotate each Riemman strip around the axis perpendicular to the strip, e.g. you rotate a vertical strip (whose top and bottom values are in terms of x) around the x axis. Giving you a disc (in this case, but more generally a washer). Rotate the same vertical strip around the y axis instead and what do you get?

Solid of revolution - Wikipedia, the free encyclopedia