Turning Derivative into Function (Newbie Question)

*To*: mathgroup at smc.vnet.net*Subject*: [mg115451] Turning Derivative into Function (Newbie Question)*From*: Just A Stranger <forpeopleidontknow at gmail.com>*Date*: Tue, 11 Jan 2011 06:58:59 -0500 (EST)

When I apply a function that outputs another function, how come I can not pass arguments to the new function? Am I missing some principle about how Mathematica functions work? Could someone please point me to the relevant documentation? A simple example to illustrate my confusion: In[1]: f[x_] := x^2 In[2]: g := f'[x] So now I have: In[3]: g out[3]: 2x as expected So how come I get the following when trying to pass an argument to g: In[4]: g[2] Out[4]: 2x[2] Instead of the output I want: *Ou[4]: 4 I tried In: g[x_] := f'[x] But it seems to think I'm trying to assign a function to Times. "SetDelayed::write: Tag Times in (2 x)[y_] is Protected. >>" Thank you very much for any help :)