Spooky maths jiggerypokery (8)

spirifer's profile

spirifer
Posted by spirifer on Wed 5 Nov 08, 6:27 PM

Maths that lies oh come on...
Let a = b
Multiply both sides by a giving
aa = ab
Then add aa - 2ab to both sides giving
aa + aa - 2ab = ab + aa - 2ab
This can be simplified to
2(aa - ab) = aa - ab
Finally divide by aa - ab and we get
2 = 1

This old chestnut came up in a thread on lies and statistics today. At fist sight it appears really persuasive and proof indeed that you can prove pretty much anything with a bit of mathematical jiggerypokery.

However, a bit of scribbling on bits of paper (and a little googling, admittedly) shows that the apparent division by (aa - ab) at the penultimate stage is in fact division by zero, since aa = ab. Division by zero is an undefined term, mathematically, apparently, and as such does not have a meaningful, sensible, or unambiguous value.

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Replies

5 Nov 08, 6:34 PM
xjames
UK(SS), 2 yrs
I can easily prove that there is no solution where n>2 to the equation x^n+y^n=z^n . Sadly there's not enough room in this box to fit it in.
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5 Nov 08, 6:35 PM
futurelife
UK, 13 mths
Hmmm! Lost me on the second line. Then algebra was never my strong point.However never have any trouble counting out the strokes,lol

5 Nov 08, 11:17 PM
mq1965
UK(DA), 5 yrs

xjames wrote:
I can easily prove that there is no solution where n>2 to the equation x^n+y^n=z^n . Sadly there's not enough room in this box to fit it in.
Thank you Mr. Fermat.

6 Nov 08, 12:19 AM
bohnanza
UK(FK), 9 yrs
Y!

mq1965 wrote:

xjames wrote:
I can easily prove that there is no solution where n>2 to the equation x^n+y^n=z^n . Sadly there's not enough room in this box to fit it in.
Thank you Mr. Fermat.
I think your thanks should be aimed at Andrew Wiles.
Science, the only religion that works even if you don't believe in it.
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6 Nov 08, 7:01 AM
Priapuss
UK(PO), 17 mths

Bottom x flogger =
Today's the tomorrow you worried about yesterday. - Faith is a certainty without evidence-trust is empirical.
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6 Nov 08, 10:02 AM
Backdooruk
UK(BA), 9 yrs

spirifer wrote:
This old chestnut came up in a thread on lies and statistics today.
Almost all issues with statistics involve people making mathematical mistakes. Statistics aren't scary because you can make them say anything (you can't) but because so many people use them while making such errors without realizing that they do.
- Chris

Anyone with a brain is manipulable. Only the truly unimaginative are difficult to control.

6 Nov 08, 10:19 AM
mq1965
UK(DA), 5 yrs

bohnanza wrote:

mq1965 wrote:

xjames wrote:
I can easily prove that there is no solution where n>2 to the equation x^n+y^n=z^n . Sadly there's not enough room in this box to fit it in.
Thank you Mr. Fermat.
I think your thanks should be aimed at Andrew Wiles.
I don't think Mr. Wiles would ever claim that he could 'easily prove' the theorem, which was, if not quite in those words, what Fermat claimed.
I seem to remember seeing a documentary about Wiles efforts to prove it, and it was far from simple. Even then he got it wrong the first time, and later had to revise his proof, though it was so complicated that no one else spotted his mistake the first time.

6 Nov 08, 5:27 PM
ropeburn
BE, 7 yrs
No elephant got hurt in the posting either


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