Quadratic polynomial can be factored using the transformation $ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right)$, where $x_{1}$ and $x_{2}$ are the solutions of the quadratic equation $ax^{2}+bx+c=0$.
$$x^{2}-9x-18=0$$
All equations of the form $ax^{2}+bx+c=0$ can be solved using the quadratic formula: $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$. The quadratic formula gives two solutions, one when $±$ is addition and one when it is subtraction.
Now solve the equation $x=\frac{9±3\sqrt{17}}{2}$ when $±$ is plus. Add $9$ to $3\sqrt{17}$.
$$x=\frac{3\sqrt{17}+9}{2}$$
Now solve the equation $x=\frac{9±3\sqrt{17}}{2}$ when $±$ is minus. Subtract $3\sqrt{17}$ from $9$.
$$x=\frac{9-3\sqrt{17}}{2}$$
Factor the original expression using $ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right)$. Substitute $\frac{9+3\sqrt{17}}{2}$ for $x_{1}$ and $\frac{9-3\sqrt{17}}{2}$ for $x_{2}$.
