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Find the positive integer n such that the expansion of (4x - 7y)^n contains a term of the form cx^2*y.

 Mar 4, 2023
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Find the positive integer n such that the expansion of (4x - 7y)^n contains a term of the form cx^2*y.

 

General term is

    \(\binom{n}{r}(4x)^r (-7y)^{n-r}\\ r=2,\\ n-2=1\qquad n=3\\~\\ \binom{3}{2}(4x)^2 (-7y)^{1}\\ \)

 

Anyway,    n=3

 Mar 4, 2023

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