Factor by Grouping am-bm+an-bn

$a m - b m + a n - b n$

Factor out the greatest common factor from each group.

Group the first two terms and the last two terms.

$(a m - b m) + a n - b n$

Factor out the greatest common factor (GCF) from each group.

$m (a - b) + n (a - b)$

Factor the polynomial by factoring out the greatest common factor, $a - b$ .

$(a - b) (m + n)$