SOLUTION: Please solve the following by factors (Please do not use the quadratic formula) 9x squared -9x-28=0

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Question 360384: Please solve the following by factors (Please do not use the quadratic formula)

9x squared -9x-28=0
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
9x squared -9x-28=0
9x%5E2+-9x-28=0
.
Find some multiple of 'a' and 'c' that
multiplies to (9)(-28) and combines to -9:
9*28
3*3*2*2*7
(-21)(12)
.
Rewrite the middle term:
9x%5E2+-21x%2B12x+-28=0
Group terms:
%289x%5E2-21x%29%2B%2812x-28%29=0
Factor:
3x%283x-7%29%2B4%283x-7%29=0
%283x-7%29%283x%2B4%29=0
x ={-4/3, 7/3}