7y(x-3y)²-2(3y-x)³=7y(x-3y)²+2(x-3y)³=(x-3y)²[7y+2(x-3y)=(x-3y)²(7y+2X-6y)=(x-3y)²(2x+y)因为 2x+y=6,x-3y=1所以 原式=1²*6=6