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Math Help - Find the coefficient of (x^7)(y^9) in the expansion of ((x-2y)^16)

  1. #1
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    Find the coefficient of (x^7)(y^9) in the expansion of ((x-2y)^16)

    Hello, I'm having trouble with this question, any help would be greatly appreciated.


    Find the coefficient of (x^7)(y^9) in the expansion of ((x-2y)^16). Write your answers as a positive or negative product of prime powers.


    Thanks.
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  2. #2
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    Re: Find the coefficient of (x^7)(y^9) in the expansion of ((x-2y)^16)

    Use the Binomial Theorem:

    (a+b)^n = \sum_{k=0}^n \binom{n}{k}a^kb^{n-k}

    Just let a = x, b = -2y, and n=16.
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