How do you factor x² - x - 90?

1 Answer
Mar 9, 2018

(x-10)(x+9)

Explanation:

To factor an expression in the form ax^2 + bx + c, find two numbers that multiply to get c and add to get b. For the expression (x^2-x-90), the factors of -90 are +-1, +-2, +-3, +-5, +-6, +-9, +-10, +-15, +-18, +-30, +-45, and +-90 (Note: +-2 means "plus or minus 2" or 2 and -2).
The only two factors that multiply to -90 and add to -1 are 9 and -10.
Thus, the factors of (x^2-x-90) are (x-10) and (x+9) or (x-10)(x+9)