# Calculus II problem: Volume of the solid

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• July 5th 2009, 10:42 PM
kn336a
Calculus II problem: Volume of the solid
Hi, I have one problem that I am completely stuck on. It is

x^2 + y^2 - 6x + 8 = 0

The problem I have is setting up the actual equation. Do I make everything in terms of y, then find where y = 0 for the points?

I tried doing this and it gave me a really funky looking graph. If anybody could point me in the right direction, that would be great!(Hi)

Thanks!
• July 5th 2009, 10:59 PM
earboth
Quote:

Originally Posted by kn336a
Hi, I have one problem that I am completely stuck on. It is

x^2 + y^2 - 6x + 8 = 0

The problem I have is setting up the actual equation. Do I make everything in terms of y, then find where y = 0 for the points?

I tried doing this and it gave me a really funky looking graph. If anybody could point me in the right direction, that would be great!(Hi)

Thanks!

Complete the squares:

$x^2 - 6x \bold{\color{red}+9}+ y^2 =- 8 \bold{\color{red}+9}$

$(x-3)^2+y^2=1$

This equation describes a circle with the center at C(3,0) and the radius r = 1
• July 6th 2009, 12:39 AM
kn336a
If I am trying to integrate that, I just have to put that in terms of dy or dx right?
• July 6th 2009, 01:04 AM
matheagle
are you trying to find volume or area?
as pointed out this is a circle in just two dimensions.
are you revolving it about a line or is there some constraints on the z-axis?
• July 6th 2009, 01:27 AM
kn336a
Sorry, here is my entire question.

Find the volume of the solid obtained by revolving the region bounded by the curve x^2 + y^2 - 6x + 8 = 0

im pretty stuck right now.
• July 6th 2009, 01:43 AM
matheagle
Quote:

Originally Posted by kn336a
Sorry, here is my entire question.

Find the volume of the solid obtained by revolving the region bounded by the curve x^2 + y^2 - 6x + 8 = 0

im pretty stuck right now.

still incomplete
revolving about what?
I'm guess either x=2, x=4, maybe the y-axis...

You need to draw this for several reasons.
First to understand the question and why it's incomplete
and later to figure out how to integrate it (shells vs. washers, dx or dy...)
NITE, it's 3:45 AM here
• July 6th 2009, 01:47 AM
kn336a
lol, so sorry. it's about the y-axis. im getting a little tired