Katy
Student
secondary

Hi i need help with some factoring. How would you factor 5x² - 27x - 18?

Hi Katy,

Since the only factors of 5 are 5 and 1, if the expression can be factored then the factored expression will have the form

(5x + a)(x + b)

Since the product of a and b is -18 the signs of a and must differ, one is positive and the other negative.

The factorizations of 18 are

1 18, 2 9, and 3 6

Now you need to go through the possibilities, one at a time, and see if you get a factorization of 5x² - 27x - 18.

Try 1 and 18

(5x + 1)(x - 18)
(5x - 1)(x + 18)
(5x + 18)(x - 1)
(5x - 18)(x + 1)

Expand each. Do and of them give 5x² - 27x - 18? If not try the next factorization of 18.

Penny