You may want to review factoring simple polynomials and factoring by grouping first.
If the polynomial you have to factor starts with a number, like 2x2 − 3x − 9, then we use the so-called AC method. We look for two numbers which add to the number in front of the x (here −3) and multiply to the product of the other two numbers (here 2 and −9, whose product is −18). These are 3 and −6. Now we can rewrite the polynomial as 2x2 + 3x − 6x − 9. (In general, we always break up the term with the x.) This can be factored by grouping, giving (2x + 3)(x − 3).
If it looks like 2x2 − 3xy − 9y2, we deal with them the same way we did with easier polynomials. In this example, say, it would factor as (2x + 3y)(x − 3y).