(3m-2n)²+(3m+2n)(3m-2n)-9(m+n)²
=(3m-2n)(3m-2n + 3m+2n )-9(m+n)²
=6m(3m-2n)-9(m+n)²
=18m(m+n)-30mn-9(m+n)²
=9(m+n)(m-n)-30mn=9m²-9n²-30mn
(3m-2n)²+(3m+2n)(3m-2n)-9(m+n)²
=(3m-2n)(3m-2n + 3m+2n )-9(m+n)²
=6m(3m-2n)-9(m+n)²
=18m(m+n)-30mn-9(m+n)²
=9(m+n)(m-n)-30mn=9m²-9n²-30mn