解：[（x+y）-3][(x-y)+3]=（x+y）(x-y)+3(x+y)-3(x-y)-9=（x+y）(x-y)+3x+3y-3x+3y-9=（x+y）(x-y)+6y-9=x²-y²+6y-9结果是：x²-y²+6y-9
