How do you factor x^2+9x+18?

1 Answer
Apr 21, 2018

By finding what multiplies to give 18 and adds to give 9.

Explanation:

General form ax^2+bx+c
What does multiplies to give ac and adds to give b

First is 18 positive or negative. If positive both factors will be positive or negative depending on the sign of b.
(Not this Question) If negative the factors will be opposite in sign.

List all the factors of ac = 18.
1,18
2,9
3,6
Now looking at these number intuitively what will add to give b = 9.

3,6

Now place into the form:
(x+6)(x+3)
This is the factorised version of x^2+9x+18

Quadratic Equation also works.