Question

Factor x2 - x - 90 = 0.
A. (x + 10)(x + 9) = 0
B. (x - 10)(x - 9) = 0
C. (x - 10)(x + 9) = 0
D. (x + 10)(x - 9) = 0

Answer 1

@iPwnBunnies

Answer 2

Do you know two numbers that multiple to give you -90 and add to give you -1?

Answer 3

\[Ax^2 + Bx + C = 0\]
C is the constant, -90. And B is the coefficient of the 'x' term, -1.

Answer 4

so its c ? && where u get -1 from

Answer 5

The -1 comes for the middle term. '...-x...'
There is an invisible 1 there. But we know it's -1.

Answer 6

It won't be D. If you FOIL choice D, you'll get ...+x... as the middle term.

Answer 7

oh, true, so it'll always be 2 numbers that the sum is -1 and when multiplied will be whatever # there is, right

Answer 8

Right. So, they need to add to -1, and multiply to give us -90.
Those two numbers are....9 and -10!

Answer 9

thank you ! your a lifesaver !