(2x-3y)(3x-2y+1)
原式=6x^2-4xy+2x-(9xy-6y^2+3y)
=6x^2-4xy+2x-9xy+6y^2-3y
=6x^2+6y^2-13xy+2x-3y
=6(x+y)^2-15xy+2x-3y