Find intervals of f increasing/decreasing

**1. The problem statement, all variables and given/known data**

(a) Find the intervals on which f is increasing or decreasing.

(b) Find the local maximum and minimum values of f.

(c) Find the intervals of concavity and the inflection points.

x2/(x2+3)

**2. The attempt at a solution**

a) I find that

f'(x)=6x/(x2+3)2

I am stuck because (x2+3)2 has no solutions and I don't know how to define x in order to proceed further.

If anybody can help me out understanding this, I will be very thankful.