I don't see a clear substitution to calculate that since when
$$u = 2x+x^2,\qquad dx = \frac{du}{2+x},$$
And so far as I've understand $dx$ shouldn't be in function of $x$ in order to calculate the integral.
I don't see a clear substitution to calculate that since when
$$u = 2x+x^2,\qquad dx = \frac{du}{2+x},$$
And so far as I've understand $dx$ shouldn't be in function of $x$ in order to calculate the integral.