Find all rational zeros of the polynomial $$P(x)=x^3 - x^2 - 9 x + 9.$$
Its rational zeros are $x_1=$ , $x_2=$ and $x_3=$ with $x_1\le x_2\le x_3$.
Note: If the polynomial has only two rational zeros, input them at $x_1$ and $x_2$; if the polynomial has only one rational zero, input it at $x_1$.