How do you factor 4x^3-28x^2-x+7?

1 Answer
EZ as pi
Jun 12, 2016

= (x - 7)(2x + 1)(2x - 1)

Explanation:

As soon as there are 4 terms, group them together in pairs first - making sure there is a PLUS sign between the pairs.
Choose the pairs so that they can be factorised further.
(4x^3 - 28^2) + (- x+ 7)

= 4x^2(x - 7) - (x - 7) " common factors "

= (x - 7)(4x^2 -1) " Diff of squares"

= (x - 7)(2x + 1)(2x - 1)

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