Simple math

Discussion in 'Math' started by boks, Dec 6, 2009.

  1. boks

    Thread Starter Active Member

    Oct 10, 2008
    218
    0
    Why is it that

    \frac{X!}{(2!)(X-2)!} - (X-1) = (\frac{X}{2} - 1)(X-1)

    ?
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    523
    The key is to multiply through by 2! This will enable you to get rid of all the factorials and the rest is simple algebra.

    Can you do it now?
     
  3. jpanhalt

    Expert

    Jan 18, 2008
    6,292
    1,173
    I just substituted X!/(X)(X-1) for (X-2)! and everything canceled out to give the answer.

    John
     
  4. StayatHomeElectronics

    AAC Fanatic!

    Sep 25, 2008
    1,021
    71
    From the definition of factorial, X!, you write out X! as X(X-1)(X-2)(X-3)(X-4)... and (X-2)! as (X-2)(X-3)(X-4)..., simplification becomes much easier.
     
  5. boks

    Thread Starter Active Member

    Oct 10, 2008
    218
    0
    Brilliant, thanks!
     
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