Dervative/ "f" prime Question. Please help!

[CalculusKid]

When there is a problem that says f (x) = 2x^2, f ' (x) = 4x. I know this. But what if it say f ' (2) = ?
Do I find the derivative then plug in the 2? If I did it the other way ( plug in the number then find the derivative), then the answer would be 0. Can someone help me please?

 

[pka]

EXAMPLE:
\(\displaystyle g'(x) = x^2 + x\quad \Rightarrow \quad g'(2) = (2)^2 + (2)\).

 

[CalculusKid]

I'm not sure I understand. Can you do this one.

f (x) = 3x^2, then f ' (5) = ?

 

[pka]

\(\displaystyle f'(5) = 6(5)\)

Tell us why that is true.

 

[stapel]

When there is a problem that says f (x) = 2x^2, f ' (x) = 4x. I know this. But what if it say f ' (2) = ?

Then do the differentiation (finding f'(x) from the expression for f(x)), and then (using what you learned back in algebra) do the plug-n-chug of the x-value in the formula for f'(x) to find f'(2).

Eliz.

 

[CalculusKid]

Thanks! I got it