Use the definition f(a)=limit

1. Nov 2, 2009

eddieberto

it tells me to use the definition

f(a)=limit..........f(a+h)-f(a)
......h->0.........__________
...........................h

to find the derivative of the given function at the indicated poin.
f(x)=1/x, a=2

I dont kno what to do

2. Nov 2, 2009

lanedance

Re: derivatives

its hard to read, try teh tex belwo (click on it)
$$lim_{h \rightarrow 0}\frac{f(a+h) - f(a)}{h}$$

try subsituting into the limit for your function evaulated at x = a, and x = a+h

3. Nov 2, 2009

eddieberto

Re: derivatives

this is how far i got and then i got lost

$$lim_{h \rightarrow 0}\frac{a-(a+h)}{h(a+h)(a)}$$
and the answer is supos to be -1/4

im lost

4. Nov 2, 2009

lanedance

Re: derivatives

you're not that far off, simplify the top line, then see what you cancel

5. Nov 2, 2009

eddieberto

Re: derivatives

thanks i got it