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Bugsbunny
Wascally
Joined: 07 Apr 2004
Posts: 7626
Location: Drinking Carrot juice
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 Posted: Mon Oct 06, 2008 5:36 am Post subject: OK - For all you geniuses :) |
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(1) X=Y ; Given
(2) X^2=XY ; Multiply both sides by X
(3) X^2-Y^2=XY-Y^2 ; Subtract Y^2 from both sides
(4) (X+Y)(X-Y)=Y(X-Y) ; Factor
(5) X+Y=Y ; Cancel out (X-Y) term
(6) 2Y=Y ; Substitute X for Y, by equation 1
(7) 2=1 ; Divide both sides by Y
What's wrong with the above proof? |
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the_hawk
Chelsea FTW!
Joined: 13 Jul 2005
Posts: 4342
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| Posted: Mon Oct 06, 2008 6:46 am Post subject: |
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In factoring out (X-Y) you effectively end up with 0/0.
Next. |
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Piemaster
Author of THE POKER MINDSET
Joined: 15 Jan 2004
Posts: 6931
Location: London
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| Posted: Mon Oct 06, 2008 12:26 pm Post subject: |
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| the_hawk wrote: | In factoring out (X-Y) you effectively end up with 0/0.
Next. |
I don't get it. At what point are you talking about? |
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Dogs
1K Club
Joined: 17 May 2006
Posts: 1176
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| Posted: Mon Oct 06, 2008 12:46 pm Post subject: |
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| Piemaster wrote: | | the_hawk wrote: | In factoring out (X-Y) you effectively end up with 0/0.
Next. |
I don't get it. At what point are you talking about? |
To go from line 4 to line 5, we are dividing both side by (x - y). As x = y, that means we are dividing by zero, making it an invalid argument. |
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Piemaster
Author of THE POKER MINDSET
Joined: 15 Jan 2004
Posts: 6931
Location: London
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| Posted: Mon Oct 06, 2008 12:59 pm Post subject: |
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| Ah I see |
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San
53o
Joined: 28 Mar 2004
Posts: 4150
Location: Cardiff, Wales
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| Posted: Mon Oct 06, 2008 1:34 pm Post subject: |
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I prefer
10(0.9r)=9.9r
9.9r - 0.9r = 9
9(0.9r) = 9
0.9r = 1
It's always great for starting arguments between people who understand mathematics (a bit, anyway) and people who don't. |
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PauliF
Shoes in Safe
Joined: 16 Jun 2004
Posts: 2787
Location: London
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| Posted: Mon Oct 06, 2008 2:38 pm Post subject: |
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there are only 10 types of people
those who understand binary
and those who dont |
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toom
Spelling Bee Champ
Joined: 06 Apr 2005
Posts: 2389
Location: Basketball season is awesome BAYBEEEEE
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| Posted: Mon Oct 06, 2008 3:41 pm Post subject: |
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| There's no place like 127.0.0.1 |
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toom
Spelling Bee Champ
Joined: 06 Apr 2005
Posts: 2389
Location: Basketball season is awesome BAYBEEEEE
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| Posted: Mon Oct 06, 2008 3:43 pm Post subject: |
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| Interesting. As soon as you subtract y^2 from both sides in step three, you end up with 0=0. |
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torch
Drunken Songmaster
Joined: 06 May 2004
Posts: 3454
Location: Centreville, VA
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| Posted: Mon Oct 06, 2008 6:06 pm Post subject: |
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Haven't looked at others responses yet - you are dividing by 0.
If X = Y, then X-Y = 0 |
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niin
ITH Software Programmer
Joined: 15 Jun 2004
Posts: 4487
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| Posted: Mon Oct 06, 2008 6:38 pm Post subject: |
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| San wrote: |
10(0.9r)=9.9r
9.9r - 0.9r = 9
9(0.9r) = 9
0.9r = 1 |
This one doesn't make sense to me, since going from step 2 to step 3 is just incorrect. I'm assuming it's an attempt to factor out a '9' from that equation, but step 3 isn't a result of that.
And for the first answer, yeah, it's becaues division by zero is undefined, thus yielding the proof invalid. You have to leave (x-y) in the equation where it is to maintain the validity of the proof, but any time you start dividing by anything, you have to have the assumption that what you're dividing by is not zero. |
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toom
Spelling Bee Champ
Joined: 06 Apr 2005
Posts: 2389
Location: Basketball season is awesome BAYBEEEEE
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| Posted: Mon Oct 06, 2008 8:05 pm Post subject: |
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I'm corn-fused by this one from the first line (my comments in bold)
| San wrote: |
10(0.9r)=9.9r shouldn't this be 10(0.9r) = 9.0r ?
9.9r - 0.9r = 9 never mind line one, surely 9.9r - 0.9r = 9.0r?
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toom
Spelling Bee Champ
Joined: 06 Apr 2005
Posts: 2389
Location: Basketball season is awesome BAYBEEEEE
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| Posted: Mon Oct 06, 2008 8:05 pm Post subject: |
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| So, does 1/3 = .33333333 (repeating)? |
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Chevin
Joined: 26 May 2004
Posts: 780
Location: UK
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| Posted: Mon Oct 06, 2008 8:20 pm Post subject: |
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Yesterday I walked into town to post a letter and have a coffee with a new book. Five steps after the post box i realized i'd posted the book and was heading for the coffee shop with the letter.
After a quick look at this thread, I can confirrm I'm teh dumbest SOB on ITH.
Night folks. |
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darvon
BCS Neutral
Joined: 28 Feb 2004
Posts: 5360
Location: Detroit
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| Posted: Mon Oct 06, 2008 8:28 pm Post subject: |
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I had the same problem years ago with a letter and my newborn.
Ahh memories.... |
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