September 12th, 2017, 04:37 PM  #1 
Member Joined: Feb 2017 From: East U.S. Posts: 40 Thanks: 0  Disk or Washer method
Hi guys, I'm having a little trouble setting this problem up: "Let R be the region bounded by the following curves. Use the disk or washer method to find the volume of the solid generated when R is revolved about the yaxis. y = x, y = 5x, y = 20" I can solve for the volume once I have the integral set up, but I'm a little confused on how to get the boundaries, as well as which function is being subtracted from the other. Normally I'll get two "y = ..." and two "x = ...", but I have three "y = ..." this time. Any tips would be great! Thank you. Last edited by nbg273; September 12th, 2017 at 04:39 PM. 
September 12th, 2017, 04:55 PM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,719 Thanks: 1374 
washers w/respect to y ... $\displaystyle A = \pi \int_0^{20} y^2  \left(\dfrac{y}{5}\right)^2 \, dy$ 

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disk, method, washer 
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