# Math Help - Summation Question

1. ## Summation Question

$\sum^{n-3}_{j=0}(2(n+j-2))$

= 2 * ( (n-2) + (n-1) + n +... + (2n-5) )

$= 2 * ( \sum^{2n-5}_{i=1}(i) - \sum^{n-3}_{i=1}(i) )$
...

I don't understand where the (2n-5) comes from in line 2, and then why we use it in the summation on line 3. Nor do I understand where those summations come from on line 3 and why we subtract them.

2. When j = n - 3, what is the simplified form of n + j - 5?

If you can simplify "n + j - 2" to be something simpler, why not?