$\displaystyle A(n) = a(1 + \frac{r}{n})^n$

Above is the formula. We were told to prove that A(n + 1) > A(n) for each positive integer n, and we were told that we need the binomial theorem. I understand the binomial theorem somewhat, but I don't know how to convert it to make the proof "correct".

Thanks, hope I'm not being too vague.