asnaseer
Puzzle: Who can spot what is wrong here?
Theorem: 4 = 5
Proof: 20 = 20
16  36 = 25  45
4^2  (9x4) = 5^2  (9x5)
4^2  (9x4) + 81/4 = 5^2  (9x5) + 81/4
(4  9/2)^2 = (5  9/2)^2
4  9/2 = 5  9/2
4 = 5



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lgbasallote
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how did you get 20=20 from 4=5

Freyes
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It's a puzzle.

asnaseer
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The Theorem states 4 = 5
It is then followed by the proof

lgbasallote
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oh that

Freyes
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the third to last step

JakeV8
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sqrt of neg?

asnaseer
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and what exactly is wrong with that step?

Freyes
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The step is squaring a negative 1/2 and the other is squaring 1/2

asnaseer
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which is fine, since (1/2)^2 = (1/2)^2

Freyes
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Yes but then the square root of that after is where the problem is

asnaseer
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correct :)

Freyes
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you're choosing the positive side

Freyes
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not the same negative part you're squaring

cwrw238
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yes  well done frees

asnaseer
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it is essentially the same as saying:
(1)^2 = (1)^2
therefore 1 = 1

asnaseer
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well spotted!

oldrin.bataku
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\[\pm[4\frac92]=\pm[5\frac92]\]