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Math Help - When is it true (x+y)^n=x^n + y^n ??

  1. #1
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    When is it true (x+y)^n=x^n + y^n ??

    When is it true (x+y)^n=x^n + y^n ?? Any thoughts?
    Last edited by mr fantastic; September 6th 2010 at 09:00 PM. Reason: Copied title into main body of question.
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  2. #2
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    It's called Child's Binomial Theorem. If n = 1, it's true. If n \ge 2, not so much. For all [LaTeX ERROR: Convert failed] , though, \displaystyle (x+y)^n = \sum_{k=0}^n {n \choose k}x^{n-k}y^k (call it Grown-up's Binomial Theorem).
    Last edited by TheCoffeeMachine; September 6th 2010 at 04:05 PM.
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    That's what I thought, only n=1. Thanks
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    Also of course when x=0 or y=0.
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