(3m-2n)^+(3m+2n) (3m-2n)-9(m+n)^

(3m-2n)²+(3m+2n) (3m-2n)-9(m+n)²=(3m-2n)²-9(m+n)²+(3m+2n) (3m-2n)=(3m-2n+3m+3n)(3m-2n-3m-3n)+9m²-4n²=-5n(6m+n)+9m²-4n²=-30mn-5n²+9m²-4n²=9m²-9n²-30mn