How do I write this function in Mathematica?

Questions
1

Hello!
I am enjoying using Mathematica on a daily basis, but as I am a newbie I do not manage to do everthing I want , yet.

How do I tell Mathematica to compute f(f(x)) when f(x)=(x+3)^2 or something like that?

Best regards,
Ulf Karlsson

2

I would do it this way:

f[x_] := (x + 3)^2;
f[f[x]]

Beware the difference between square brackets and round parentheses, and between the pattern x_ and the variable x.

3

Basically,

f[x_]:=(x+3)^2

would define a function of the variable x. Such that f[1]=16 and f[-1]=4 etc.
Then you can write f[f[x]]

You can also write

f@f@x

See here and here. This latter link is a good resource in my opinion.

Good luck!

And glad to help.

4

Thanks!

//Ulf

5

Thanks!

//Ulf