# first principles

• Feb 5th 2008, 06:42 PM
CenturionMonkey
first principles
Hey i need help with this question:

Find the derivative of the function $f(x)=1/(x+2)$ by using first principles.

We have to use first principles, please and thanks you.
• Feb 5th 2008, 07:37 PM
Krizalid
If the limit exists, then

$f'(x) = \mathop {\lim }\limits_{\Delta x \to 0} \frac{{f\left( {x + \Delta x} \right) - f(x)}}
{{\Delta x}}.$

And $f\left( {x + \Delta x} \right) = \frac{1}
{{\left( {x + \Delta x + 2} \right)}}.$
You may perform from there the calculations.