Michael J. answered • 11/14/15
Tutor
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Effective High School STEM Tutor & CUNY Math Peer Leader
To factor by grouping, we put all the terms that have common factors together.
20x3 - 28x2 + 15x - 21 =
4x2(5x - 7) + 3(5x - 7)
Notice that the GCF is (5x - 7).
(5x - 7)(4x2 + 3)
