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September 12th, 2017, 04:37 PM   #1
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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‚Äč y-axis. 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.
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September 12th, 2017, 04:55 PM   #2
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washers w/respect to y ...

$\displaystyle A = \pi \int_0^{20} y^2 - \left(\dfrac{y}{5}\right)^2 \, dy$
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