# Calc Derivative Question

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• January 20th 2009, 02:57 PM
Sculthorp
Calc Derivative Question
Hey! How do you find the derivative of the following using the first derivative principles?

a) f(x)=7/x-x
b) f(x)=(x+1)^1/2
• January 20th 2009, 02:59 PM
Jhevon
Quote:

Originally Posted by Sculthorp
Hey! How do you find the derivative of the following using the first derivative principles?

a) f(x)=7/x-x
b) f(x)=(x+1)^1/2

use the formula, there are two, the usually used as far as i can see is

$f'(x) = \lim_{h \to 0} \frac {f(x + h) - f(x)}h$

Hint: for the second problem, multiply by the conjugate of the numerator over itself to simplify

can you finish?
• January 20th 2009, 03:04 PM
Sculthorp
Thanks for the help! The problem is with the 7/x-x I get 7/0 which is not possible right? So.... is this not possible to get the derivative?
• January 20th 2009, 03:23 PM
skeeter
I don't think the function is $\frac{7}{x-x}$ ... most probably it's $\frac{7}{x} - x$