# Binomial Coefficient problem

I'm working on an IB mathematics portfolio, and here's a problem I don't understand:
The formula for the general term is
$$T_n+1=C_n^r a^{n-r} b^r$$
Verify this formula by examples. This is the formula for the $(r+1)$-th term.
What would the formula for the $r$-th term be?
It's not specified what $a$ and $b$ is supposed to represent. That's where I need some explanation.
I already made a nice Pascal triangle all the way to the 10th row.
All help is appreciated.

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dextercioby
Homework Helper
My guess is that it comes from the expansion:

$$(a+b)^{n}=\sum_{k=0}^{n}C_{n}^{k} a^{n-k}b^{k}$$

Daniel.

PS.Can u handle the $(n-1)$ term part??

Thanks, I'll give it a try