How do you factor #6 + 7x - 20x^2#?

1 Answer
EZ as pi
Oct 9, 2017

#6-7x-20x^2 = (3-4x)(2+5x)#

Explanation:

Find factors of #6 and 20# which differ by #7#

#" "6" "20#
#" "darr" "darr#

#" "3" "4" "rarr 2 xx 4 = 8#
#" "2" "5" " rarr 3xx5 =ul15#
#color(white)(xxxxxxxxxxxxxxxxx)7#

We have the correct factors, now add in the signs.

We need #-20# and #+7#

#" "3" "-4" "rarr 2 xx -4 = -8#
#" "2" "+5" " rarr 3xx+5 =+ul15#
#color(white)(xxxxxxxxxxxxxxxxxxxxx)+7#

#6-7x-20x^2 = (3-4x)(2+5x)#

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