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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 :)