Derivative of f(x)=1/x at x=2 using the Limit Definition

[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 don't kno what to do

 

[lanedance]

its hard to read, try the 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

 

[eddieberto]

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

 

[lanedance]

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

 

[eddieberto]

thanks i got it