# Math Help - Simplifying sigma

1. ## Simplifying sigma

Hello I need help with this question:

If f(x) is a funciton of x, defined for all nonnegative integers, simliplify the sum $\sum_{i=1}^n[ (f(i) - f(i-1)]$

My attempt: $\sum_{i=1}^n[f(i)]- \sum_{i=1}^n]f(i-1)]$

Then i kind of expanded f (i-1) in wrongly by saying it's equal to f(i) - f(1).
My final answer is wrong because of this assumption.
Where should I go from here?

2. ## Re: Simplifying sigma

I'd start by writing out the first few terms of each sum. You might see something cool happen...