How do you factor x312x2+41x42?

1 Answer
Jun 14, 2018

(x2)(x3)(x7)

Explanation:

If the roots of the cubic are integer, then they must divide into 42. Possible candidates, plus or minus: 1, 2, 3, 6, 7, 14, 21, 42.

A little exploration with a calculator reveals that both x=2 and x=3 are roots, so we can immediately factor the expression as
(x2)(x3)(x7), deducing from 42=237 that the third root must be 7.