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)