1. If the graph of the function $f(x)=\left(x^{2}-a x+2 a\right) \ln (x+1)$ passes through four quadrants, then the range of the real number $a$ is $\qquad$ .
1. $\left(-\frac{1}{3}, 0\right)$.

When $x>0$, $\ln (x+1)>0$; when $-10, g(0)<0$. The solution for the range of real number $a$ is $\left(-\frac{1}{3}, 0\right)$.