December 28th, 2012, 06:11 PM  #1 
Newbie Joined: Jun 2012 Posts: 15 Thanks: 0  When do I use the washer method?
Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified line. y=x^2 , x=y^2; about y=1 Why is the area: A(x)=Pi[(1x^2)^2(1sqrt(x))^2]? I know how to do the problem, but I want to know where the is 1  X^2 coming from? Whis is there a 1  in front? When Do I know when I have to use it? 
December 28th, 2012, 06:45 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 463 Math Focus: Calculus/ODEs  Re: When do I use the washer method?
For an arbitrary washer, the outer radius is the distance between the axis of rotation and the curve , while the inner radius is the distance between the axis of rotation and the curve . As far as when to use the washer method, do so if instructed, or if given a choice, when it is easier to compute than the shell method. I recommend using both methods though, to check your work, and for practice using either method. 
December 28th, 2012, 06:54 PM  #3 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,642 Thanks: 960 Math Focus: Elementary mathematics and beyond  Re: When do I use the washer method?
I get .

December 28th, 2012, 06:54 PM  #4  
Newbie Joined: Jun 2012 Posts: 15 Thanks: 0  Re: When do I use the washer method? Quote:
 
December 28th, 2012, 06:55 PM  #5  
Newbie Joined: Jun 2012 Posts: 15 Thanks: 0  Re: When do I use the washer method? Quote:
 
December 28th, 2012, 06:57 PM  #6  
Newbie Joined: Jun 2012 Posts: 15 Thanks: 0  Re: When do I use the washer method? Quote:
 
December 28th, 2012, 07:06 PM  #7 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,642 Thanks: 960 Math Focus: Elementary mathematics and beyond  Re: When do I use the washer method? 
December 28th, 2012, 07:14 PM  #8  
Newbie Joined: Jun 2012 Posts: 15 Thanks: 0  Re: When do I use the washer method? Quote:
Remember its about Y=1!  
December 28th, 2012, 07:16 PM  #9 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,642 Thanks: 960 Math Focus: Elementary mathematics and beyond  Re: When do I use the washer method?
Where did you get that answer?

December 28th, 2012, 07:20 PM  #10  
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 463 Math Focus: Calculus/ODEs  Re: When do I use the washer method? Quote:
I get .  

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