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December 28th, 2012, 06:11 PM   #1
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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[(1-x^2)^2-(1-sqrt(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?
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December 28th, 2012, 06:45 PM   #2
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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.
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December 28th, 2012, 06:54 PM   #3
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Re: When do I use the washer method?

I get .
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December 28th, 2012, 06:54 PM   #4
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Re: When do I use the washer method?

Quote:
Originally Posted by MarkFL
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.
Yes but when do I know when to put 1- in front of the function in area? What should the question day then?
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December 28th, 2012, 06:55 PM   #5
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Re: When do I use the washer method?

Quote:
Originally Posted by greg1313
I get .
Check your answer.
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December 28th, 2012, 06:57 PM   #6
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Re: When do I use the washer method?

Quote:
Originally Posted by MarkFL
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.
When should I know when a cross section with a washer needs to have 1 - in front of it? That is my question.
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December 28th, 2012, 07:06 PM   #7
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Re: When do I use the washer method?



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December 28th, 2012, 07:14 PM   #8
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Re: When do I use the washer method?

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No the answer should be 11/30(Pi)

Remember its about Y=1!
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December 28th, 2012, 07:16 PM   #9
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Re: When do I use the washer method?

Where did you get that answer?
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December 28th, 2012, 07:20 PM   #10
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Re: When do I use the washer method?

Quote:
Originally Posted by mortified_penguin
Quote:
Originally Posted by MarkFL
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.
Yes but when do I know when to put 1- in front of the function in area? What should the question day then?
The distance between the axis of rotation (y = 1 in this case) and some function beneath it is 1 - f(x). The "1 -" comes from that distance.

I get .
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