How do you factor the expression #5x^2 - 21x + 18#?

1 Answer
EZ as pi
Mar 9, 2018

#(5x-6)(x-3)#

Explanation:

#5x^2 -21x+18#

Find factors of #5 and 21# whose products ADD to #21#
There is often a bit of trial and error, keep trying different combinations.

The signs will both be the same (because of #+18#), they will both be #-#.

#" "5" "18#
#" "darr" "darr#
#" "5" "6" "rarr 1xx6 =6#
#" "1" "3" "rarr 5xx3 = ul15#
#color(white)(xxxxxxxxxxxxxxxxx)21#

Top row gives one bracket and second row gives the other bracket.

#(5x-6)(x-3)#

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