I have to explore function $\frac{2x-4}{1+x^2}$ It contains finding definition area of function, finding roots etc. One of the points is to find inflection points and concavity of function. I cannot find it.
I have found out first and second derivative of function. From first derivative I find out two points where f(x)'=0. $x1=(2+\sqrt{5})$ and $x2=(2-\sqrt{5})$
Then I have tried to find second derivative and it is: $\frac{4x^3-24x^2-12x+8}{(x^2+1)^3}$. I beleive I have to solve f(x)''=0 to find something about functions concavity, but I cannod do it.