How do I go about calculating the sum of this finite series? Below is the series and the sum:
$$\sum_{i=0}^{n^2-1}i$$
I understand that you have to use the formula: $\sum_{i=1}^{n}i = \frac{n(n+1)}{2}$ and that the answer is: $\frac{n^4-n^2}{2}$. I just don't know the steps to get there. I'm being thrown off by the starting index of $i=0$.