Factor using the ac-method.
-$21 x^{2}-91 x-70$
A) $7(3 x+2)(x-5)$
B) $7(3 x-2)(x+5)$
C) prime
D) $(21 \mathrm{x}+14)(\mathrm{x}-5)$

Question

Quizplus · Accepted Answer

The ac-method involves multiplying 'a' and 'c' (from ax^2+bx+c) and finding two numbers that multiply to ac and add to b. Here, ac = 21*(-70) = -1470, and we need two numbers that multiply to -1470 and add to -91. Those numbers are -105 and 14. Factoring by grouping with these numbers gives us 7(3x+2)(x-5).

Factor Using the Ac-Method 21x2−91x−7021 x^{2}-91 x-7021x2−91x−70 A) 7(3x+2)(x−5)7(3 x+2)(x-5)7(3x+2)(x−5) B) 7(3x−2)(x+5)7(3 x-2)(x+5)7(3x−2)(x+5)

Factor Using the Ac-Method $21 x^{2}-91 x-70$ A) $7(3 x+2)(x-5)$ B) $7(3 x-2)(x+5)$