How do you factor # 3x^2 - 7x - 20#?

1 Answer
EZ as pi
Jul 6, 2016

#(3x +5)(x -4)#

Explanation:

#color(Blue)3x^2 color(purple)-color(green)7x color(red)-color(blue)20#

Find the factors of #color(blue)(3 and 20)# which #color(red)"(SUBTRACT)"# to give #color(green)7#.

The signs will be #color(red)"DIFFERENT"#, there must be more #color(purple)"negatives"#

Find the factors and try different combinations. Cross multiply and find the difference until you get 7.

#"3 +5 "rArr 1 xx+5" +5"#
#"1 -4 "rArr3 xx-4" -12"#
#" "-7#

#(3x +5)(x -4)#

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