2x²+(-x²+3xy+2y²)-(x²-xy+2y²)=2x²-x²+3xy+2y²-x²+xy-2y²=4xy
因为|x-2|与[y-(1/3)x]²互为相反数,所以|x-2|=0,既x=2;[y-(1/3)x]²=0,既y=2/3
则4xy=4*2*2/3=16/3