To factor by a binomial, I like to use synthetic division (You can use long division but it is more work).
We are actually given a binomial because if -2 is a zero, the binomial is represented by (x- (-2)) or (x+2)
To use synthetic division,
-2 | 1 2 -9 -18
-2 0 18
____________
1 0 -9 0
Therefore, you know the constants of the equation which is equal to
1x^2 +0x -9x +0
x^2-9x
The full equation is equal to (x+2)(x^2-9x)