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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