Here's the question you clicked on:
Grazes
Find the middle term of the binomial expansion of (3a-b)^10
n+1 terms, so 11 terms. 6th term, I guess
I know the answer, but I was wondering if there was a method to solve it without guessing/inferring what the i-1 of \[\left(\begin{matrix}n \\ i-1\end{matrix}\right) a ^{n-(i-1)} b ^{i-1}\] is.
I copied it verbatim from my textbook o-o
if you substitute i-1 with k, it's right. Mine formula is just so that i can equal the nth term. Your n(th term) would need to be decreased by 1. Just technicalities.
errr nevermind. I chose a bad example. You just substitute the given values in this one.