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**NoSash****Member**- Registered: 2006-02-06
- Posts: 7

1) 16 - 36 = 25 - 45

2) 16 - 36 + 81/4 = 25 - 45 + 81/4

3) 4^2 - 2x4x9/2 + (9/2)^2 = 5^2 - 2x5x9/2 + (9/2)^2

4) (4 - 9/2)^2 = (5 - 9/2)^2

5) 4 - 9/2 = 5 - 9/2

6) 4 = 5

What went wrong?

I'm pretty sure the error is from step 3 to 4 but I don't know what the heck they are trying to do.

*Last edited by NoSash (2006-02-06 10:57:55)*

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**darthradius****Member**- Registered: 2005-11-28
- Posts: 97

when you take the square root, you need the ± which gives you a few different combinations...this "proof" just uses one combination that does not work.

The greatest challenge to any thinker is stating the problem in a way that will allow a solution.

-Bertrand Russell

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**krassi_holmz****Real Member**- Registered: 2005-12-02
- Posts: 1,908

e.a.

4) (4 - 9/2)^2 = (5 - 9/2)^2

5) |4-9/2|=|5-9/2|

6) |-0.5|=|+0.5|

which is OK.

*Last edited by krassi_holmz (2006-02-06 18:57:47)*

IPBLE: Increasing Performance By Lowering Expectations.

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**kempos****Member**- Registered: 2006-01-07
- Posts: 77

step 5. there you should have absolute value.

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**krassi_holmz****Real Member**- Registered: 2005-12-02
- Posts: 1,908

Yep.

IPBLE: Increasing Performance By Lowering Expectations.

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

All of the above is correct. They've hidden it with lots of unnecessary complications, but what they're basically doing is saying that as x² = (-x)², then x = -x, even though it doesn't.

Why did the vector cross the road?

It wanted to be normal.

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**NoSash****Member**- Registered: 2006-02-06
- Posts: 7

yeah it all makes sense, thanks guys

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**NoSash****Member**- Registered: 2006-02-06
- Posts: 7

Hey guys, apparently it's incorrect to put the absolute value signs, can anybody confirm this? Or support it? I know it works out mathematically but I was told it's still wrong.

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