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March 21st, 2009, 03:27 AM   #1
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Derivative function - how do I insert values?

Hi

I have the derivative function:

f'(x)= lim h->0 = [ f(x+h)-f(x) ] / h

The question is:

Find from the first principles the gradient of f(x) where f(x) is: a) x b) 5 c) x^3

My problem is, I have no idea how I insert these values into the formula...?

If someone shows me how to do this step by step I would be very thankful!!
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March 21st, 2009, 05:19 AM   #2
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Re: Derivative function - how do I insert values?

Plug in x+h for x in f(x+h). Like so. I will use x^3



Expand:



Canceling the h's and leaving those that remain approach 0, leaves us with:

, which is the derivative of .
 
March 21st, 2009, 07:42 AM   #3
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Quote:
Originally Posted by toulouse
f'(x)= lim h->0 = [ f(x+h)-f(x) ] / h

Find from the first principles the gradient of f(x) where f(x) is: a) x b) 5 c) x^3

My problem is, I have no idea how I insert these values into the formula...?
Ouch! They were supposed to have covered that topic back in algebra!

To learn how, try studying some lessons on function notation.

Short version: Whatever they want you to evaluate at (like x, 5, or x^3), plug that in for every "x" in your function formula.
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