# Proff of the Numerical Derivative

1. Jul 31, 2009

### Jimmy84

1. The problem statement, all variables and given/known data

Proff that f´(x) = the lim of delta x approaching to 0 of

f (a + delta x) - f (a -delta x) / 2 delta x

2. Relevant equations

3. The attempt at a solution

the book hinted me that I should solve it in this way

f (a + delta x) - f (a) + f (a) - f (a - delta x) / 2 delta x

but im stuck here and I dont know how to proff this. I d appreciate some help, thanks a lot in advance.

2. Jul 31, 2009

### D H

Staff Emeritus
The word is prove, not proff.

Anyhow, try it with

$$\frac 1 2 \,\frac {f(a+\Delta x) - f(a) \,\,\,+\,\,\, f(a) - f(a-\Delta x)}{\Delta x}$$