(2x+3y+2)(2x-3y+6)
=[(2x+4)+(3y-2)]*[(2x+3)-(3y-2)]
=(2x+4)^2-(3y-2)^2
=(4x^2+16x+16)-(9y^2-12y+4)
=4x^2-9y^2+16x+12y+12