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November 28th, 2008, 07:44 PM   #1
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Why doesn't this work?

The answer is supposed to be 8. The answer is 8 when we use a computer program.

When we integrate on pen and paper, it is 0. Why doesn't my technique work? We can't figure it out

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November 29th, 2008, 05:08 AM   #2
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Re: Why doesn't this work?

The image is not coming through for me except in tiny unreadable form, so I can't see what you might have done. However, I must add that if it is really for extra credit, then you really, REALLY should not seek outside help of any sort. Otherwise the purpose of determining your own special skills is entirely defeated.
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November 29th, 2008, 11:45 AM   #3
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Re: Why doesn't this work?

http://img20.imageshack.us/my.php?image ... ditko6.jpg

That link isn't working for you?

Also, the "deal" is we figure it out on our own. So obviously, I have done the hard work. I showed her and she said that she can't figure out why my method doesn't work so I should ask for help.
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November 29th, 2008, 12:35 PM   #4
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Re: Why doesn't this work?

The problem occurs because

When you make the subs, you probably get something like ...Correct?.

Break it up and integrate over

You will get 8.
 
November 29th, 2008, 12:41 PM   #5
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Re: Why doesn't this work?

Hey, I have been doing that only with ?/2 instead of 3?/2. Why are we differing there?

Also, don't you have to put the limit as n approaches 3?/2?

Also, do you think my "hint" would work this way?
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November 29th, 2008, 01:01 PM   #6
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Re: Why doesn't this work?

Because equals 0 at

At Pi/2 it equals 2.
 
November 29th, 2008, 01:39 PM   #7
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Re: Why doesn't this work?

So I did it my way again replacing ?/2 with 3?/2 and I am not getting the right answer, so there must be something wrong with my way other than wrong limits. I will try your way.
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November 29th, 2008, 02:23 PM   #8
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Re: Why doesn't this work?

Did you look at the graph?. Take a look and see why it is a good idea to break it up.
That is why when you integrate straight from 0 to 2Pi, you get 0. See at 3Pi/2 it equals 0.
You get 0 because of the absolute value.
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File Type: jpg sine4.jpg (20.3 KB, 130 views)
 
November 29th, 2008, 07:29 PM   #9
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Re: Why doesn't this work?

Quote:
Originally Posted by dottywine
http://img20.imageshack.us/my.php?image=mathextracreditko6.jpg

That link isn't working for you?

Also, the "deal" is we figure it out on our own. So obviously, I have done the hard work. I showed her and she said that she can't figure out why my method doesn't work so I should ask for help.
The "deal" is this is the internet and I can't read your mind. You could have made that clear at the start. Anyhow, you have your help.
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November 29th, 2008, 10:57 PM   #10
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Re: Why doesn't this work?

What a deal! Not bad for $32.50 a month!
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