Composition functions

So I think I've got it....

I believe the y function is doing the square root so...

f(u) = x+4

g(x)= x^2

??

Try  \(g(x)=x^2+4\)  and  \(f(u)=\sqrt u\)

or  \(g(x)=x^2\)   and  \(f(u)=\sqrt{u+4}\)

or ...

Express the function \(\sqrt{x^2+4}\) as a composition of y=f(g(x)) of the two simpler functions y= f(u) and u=g(x}

f(u)=

g(x)=

I know how to put a function into another function but I don't know what this thing is asking :S

.     \(y=\sqrt{x^2+4}\)

.     \(y=Root\ from \ ( x^2+4)\) 

.               u                    g

f(u)=\(\sqrt{g(x)}\)

\(g(x)=(x^2+4)\) 

I hope I could help.

  !

.  

Alan was correct with, g(x)=x^2+4 and f(u)=sqrt(u)