Find the coefficient of `a^3b^4c` in the expansion of `(1+a-b+c)^9dot`
Find the coefficient of `a^3b^4c` in the expansion of `(1+a-b+c)^9dot`
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`(1+a-b+c)^(9) = sum(9!)/(n_(1)!n_(2)!n_(3)!n_(4)!).(1)^(n_(1))(a)^(n_(2))(-b)^(n_(3))(c )^(n_(4))`
For `a^(3)b^(4)c, n_(2) = 3, n_(3) = 4, n_(4) = 1` and `n_(1) = 1`.
`:.` Coefficient of `a^(3)b^(4)c = (9!)/(1! xx 3! xx 4! xx 1!) = (9!)/(3! xx 4!)`
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