原式=3x（2x-y-2）+3xy+6x+xy-2y2+2x-8y-8=3x（2x-y-2）+4xy-2y2+8x-8y-8=3x（2x-y-2）+2y（2x-y-2）+2y2+4y-2y2+8x-8y-8=3x（2x-y-2）+2y（2x-y-2）+8x-4y-8=3x（2x-y-2）+2y（2x-y-2）+4（2x-y-2）=（2x-y-2）（3x...