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Math Help - it lost me

  1. #1
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    Wink it lost me

    What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?
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  2. #2
    Bar0n janvdl's Avatar
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    Quote Originally Posted by lkrb View Post
    What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?
    Just use the binomial theorem.
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by lkrb View Post
    What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?
    Quote Originally Posted by janvdl View Post
    Just use the binomial theorem.
    correct. to be more specific. the formula for binomial expansion is:

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

    though i much prefer it in the order (it's exactly the same thing) of \sum_{k = 0}^{n} {n \choose k}a^{n - k}b^k


    Here you have a = 3x and b = 2y, and you want the term given by k = 9 (using the second formula)
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  4. #4
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    Just like guys here mentioned... you use binomial theorem. So your final answer would be [17! / (8! * 9!)] * (3^8) (2^9).
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