Results 1 to 7 of 7

Math Help - Funny little thing i stumpled upon

  1. #1
    Member
    Joined
    May 2010
    Posts
    98

    Funny little thing i stumpled upon

    a=b => a^2=ab =>a^2-b^2=ab-b^2=> (a+b)(a-b)=b(a-b) => a+b=b =>2b=b => 2=1

    It's pretty simple to find the 'error', but a funny equation to show students
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by Zaph View Post
    a=b => a^2=ab =>a^2-b^2=ab-b^2=> (a+b)(a-b)=b(a-b) => a+b=b =>2b=b => 2=1

    It's pretty simple to find the 'error', but a funny equation to show students
    I remember it being funny at first but got old pretty quickly. There's some discussion on this thread. I post this mainly to prevent a repeat thread.

    By the way, you can get nicer implication arrows using \Rightarrow \Rightarrow
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    May 2010
    Posts
    98
    Ow, sorry for repost then , im fairly new to this forum, so.. Thanx for the TeX help though
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by Zaph View Post
    Ow, sorry for repost then , im fairly new to this forum, so..
    Not sure what the "Ow" was meant to represent.. some comments in the other thread were a bit harsh, and I certainly didn't mean to make you feel like you'd stepped out of line or posted something dumb. It's good to realise though that to people experienced in mathematics, the errors in these types of "proofs" tend to stand out immediately and appear rather silly.

    Quote Originally Posted by Zaph View Post
    Thanx for the TeX help though
    You're welcome!
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member Bacterius's Avatar
    Joined
    Nov 2009
    From
    Wellington
    Posts
    927
    It's good to realise though that to people experienced in mathematics, the errors in these types of "proofs" tend to stand out immediately and appear rather silly.
    Well it can be shown that if you come up with a result that contradicts the original axioms used, then either somehow you made the axioms fail in your line of thinking, either you failed in your line of thinking. The first case hasn't been stumbled upon yet ... and I wonder if it can be proved that they can't fail *accidentally*

    But yes, it's quite fun sometimes to check out those "failproofs". You can check out this link, there is a more subtile version of the same contradiction, which is quite harder to see and a lot more interesting IHMO.

    Googling "Fallacious proof" also returns a lot of interesting results
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by Bacterius View Post
    The first case hasn't been stumbled upon yet ... and I wonder if it can be proved that they can't fail *accidentally*
    See Gödel's second incompleteness theorem.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Super Member Bacterius's Avatar
    Joined
    Nov 2009
    From
    Wellington
    Posts
    927
    Quote Originally Posted by undefined View Post
    Oh, what ? How could I forget Gödel's ? I need to remember my mathematics ... Thanks though.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Funny math cartoons
    Posted in the Math Forum
    Replies: 20
    Last Post: March 14th 2012, 12:55 PM
  2. Funny Munny
    Posted in the Math Topics Forum
    Replies: 0
    Last Post: May 29th 2011, 06:27 AM
  3. Funny problem. What is cos(pi/2) in matlab?
    Posted in the Math Software Forum
    Replies: 8
    Last Post: January 29th 2010, 09:07 AM
  4. Replies: 1
    Last Post: December 6th 2009, 11:00 PM
  5. Funny problem I had...
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: October 22nd 2007, 09:36 AM

Search Tags


/mathhelpforum @mathhelpforum