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I feel like a dunce. I can't find the error

  1. May 24, 2012 #1
  2. jcsd
  3. May 24, 2012 #2
    In line 7, B - C - A = 0. The equation A*0 = B*0 does not imply that A = B.
  4. May 24, 2012 #3


    User Avatar
    Science Advisor

    The use of A, B and C is to obfuscate what is going on. If you substitute in the values, it is obvious.

    Line 7:
    [tex]A(B-C-A) = B (B-C-A)[/tex]
    He then divided by B-C-A.

    But B-C-A = 0, and so Line 7 is nothing more than
    [tex]4 \times 0 = 5 \times 0[/tex]
  5. May 24, 2012 #4
    I see.
    So the lesson learned here is that when deviding both sides of an equation by anything the resulting equation is only valid where that thing ≠0
  6. May 24, 2012 #5


    Staff: Mentor

    A shorter way of saying that is that you can't divide both sides of an equation by zero.
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