# How to define function different in Mathematica

I want to define function in Mathematica on different way. Actually, if I already have functions a and b. How can I print the value in some point of function f but without defining functions a and b like f. I dont want to use this before a[x_]:=..., b[x_]:=... because a and b I obtained different and I can not change everything above in my code because of this.

``````  a = x;
b = 2*x;

f[x_] := a + b;
f[2]
``````
-
The output from this is `3 x`. Isn't this what you want? It is not at all clear what you are asking. – Verbeia Jan 16 '12 at 14:14
I want value of function in point 2, I need f[2], but I got the function – Pipe Jan 16 '12 at 15:00

Use `Set` instead of `SetDelayed`, like this:

``````a = x
b = 2*x

f[x_] = a + b
f[2]
``````

Be sure to read the documentation on this to understand the implications of using one or the other.

-
@Szabolics Thanks, I will. I must put stronger question because of negative points. – Pipe Jan 16 '12 at 15:50