1. x^3-6x^2y+12xy^2-8y^3+1=(x-2y)(x^2+2xy+4y^2)+6xy(2y-x)+1 =(x-2y)(x^2-4xy+4y^2)+1 =(x-2y)^3+12. M=3x^2-2xy+y^2 N=2x^2+xy-3y^2M-N=x^2-3xy+4y^2M+N=5x^2-xy-2y^2