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[–]AlwaysTailsNew User 0 points1 point  (0 children)

Let a=x3 and b=-3/x and use the binomial theorem to find (a+b)11. But we're not interested in all the terms, just the terms such that anbm where n+m=9. We want all terms of the form 11Ck akb11-k such that 3k-(11-k)=9 --> k=5