I first saw this thing (admittedly much to late in life) in a third year class entitled non-linear dynamics and chaos theory. There if i am remembering correctly we used to look for non-zero terms to figure out what kind of sink/source we had basically keep going through the theorem until you found a non-zero term and you could use that to figure out what happened near a sink/source. I have seen a few formulas of this theorem in my time one obviously being the single variable and one being the multivariable theorem the last one i have seen im less sure what to call it and i have never used it.
$ \dfrac {n!}{k!(n-k)!} $ which is equivalent to $ \dfrac {n(n-1)\cdots(n-k+1)} {k!}$
Which honestly took me awhile to figure out that these two were equivalent.
Noticing $ 0 \leq k \leq n $ where it was written and realizing $n$ and $k$ were integers helped a lot.
I guess what im looking for is some material/book with some problems (and preferably worked out solutions) involving the binomial theorem being applied in different ways and forms any recommendations appreciated.