
Kenneth S. answered 04/06/16
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Expert Help in Algebra/Trig/(Pre)calculus to Guarantee Success in 2018
Just use synthetic division (put "3" in the notch):
3| 2 -11 12 9
6 -15 -9
2 -5 -3 0
Since synthetic division (for ÷ by (x-3) yields the above remainder 0, (x-3) is indeed a factor of the cubic polynomial.