Question

Determine the factors of x2 − 6x − 8.

Prime

(x + 4)(x − 2)

(x − 4)(x + 2)

(x + 8)(x − 1)

Answer 1

foil them

Answer 2

How to FOIL the first option? :D

Answer 3

\[x^2 − 6x − 8\]

what multiplies to -8 but adds to -6

Answer 4

Multiplies to -8 :
-1 * 8 = -8
-2 * 4 = -8
1 * -8 = -8
2 * -4 = -8

Adds to -6 :
-1 + 8 = 7
-2 + 4 = 2
1 + -8 = -7
2 + -4 = -2

Answer 5

You could check the discriminant. If b^2 - 4ac isn't a perfect square, you won't get rational roots, i.e., it will be prime.

Answer 6

In this case, the discriminant seems to be about 68, which would indicate irrational roots. The quadratic is prime.

Answer 7

The above generalizations will hold true for integer coefficients.

Answer 8

@jen1511 do you understand?