How do you factor 5a² -7ab -6b²?

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Answer 1 · 2015-05-31T11:44:58

Use a version of the AC method.

$A=5$ , $B=7$ , $C=6$

Attempt to find a pair of factors of $AC=5xx6=30$ whose difference is $B=7$ . The pair $10, 3$ works.

Now use that pair to split the middle term and factor by grouping...

$5a^2-7ab-6b^2$

$=5a^2-10ab+3ab-6b^2$

$=(5a^2-10ab) + (3ab-6b^2)$

$=5a(a-2b)+3b(a-2b)$

$=(5a+3b)(a-2b)$