factoring. x^2+x-72?

Answer 1

(x-8)(x+9)

Answer 2

1. Okay, you know the answer will be in the format (x+a)(x+b).

2. Since the last sign in the equation is negative, you know one of the factors must involve subtraction. This is because a negative and postive multiply to create a negative.

3. Now we need to think of factors of 72. There is 1,2,3,8,9,24, 36, and 72. We use trial and error to see which of those will get us the desired answer.
(x+3)(x-24) would give us x^2+3x-24x-72. That's wrong
(x+8)(x-9) would give us x^2+8x-9x-72. That's wrong, but it's close. By changing the signs, we arrive at the right answer:
(x-9)(x+8)=x^2-9x+8x-72.

4. If you're having trouble with factoring, remember the FOIL method. To get from the factors to the equation, multiply the FIRST terms in each factor, multiply the OUTSIDE terms in each factor, multiply the INSIDE terms in each factor, and multiply the LAST terms in each factor.

First Outside Inside Last = FOIL method

Good luck!

Answer 3

x^2+x-72

need to multiply to -72 and add to 1
-8 and +9
(x-8) (x+9)

Answer 4

x^2+9x - 8x - 72
x(x+9) -8 (x+9)
(x+9) (x-8)