Math Is Fun Forum

1q2w3e4

Member

Registered: 2009-01-11

Posts: 10

1+1=1

I heard that you can prove that one plus one equals one! How?

TheDude

Member

Registered: 2007-10-23

Posts: 361

Re: 1+1=1

You cannot "prove" that 1 + 1 = 1, since it's not true.  You can give a false proof that most people with limited mathematical knowledge would not catch, but it's nothing more than a magic trick.

x = y
x^2 = xy
x^2 - y^2 = xy - y^2
(x + y)(x - y) = y(x - y)
x + y = y
y + y = y
1 + 1 = 1

A good exercise would be to figure out where the mistake in this "proof" is.

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Wrap it in bacon

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,385

Re: 1+1=1

1q2w3e4 ,
Are you interesting in knowing where the flaw lies?

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

tobi's a good boy

Member

Registered: 2008-08-14

Posts: 32

Re: 1+1=1

1+1=1 is real

1q2w3e4

Member

Registered: 2009-01-11

Posts: 10

Re: 1+1=1

And hoe is that?

Suyog

Member

Registered: 2009-01-14

Posts: 2

Re: 1+1=1

x = y
x^2 = xy
x^2 - y^2 = xy - y^2  ----------  here 0 = 0
(x + y)(x - y) = y(x - y)  --------  divide by 0 is undetermined
x + y = y
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