解
2A-[B-(B-A)+2A+B]
=2A-[B-B+A+2A+B]
=2A-(B+3A)
=-B-A
=-(x²+2xy+y²-3)-(x²-2xy+y)
=-x²-2xy-y²+3-x²+2xy-y
=(-x²-x²)+(2xy-2xy)-y²-y+3
=-2x²-y²-y+3
解
2A-[B-(B-A)+2A+B]
=2A-[B-B+A+2A+B]
=2A-(B+3A)
=-B-A
=-(x²+2xy+y²-3)-(x²-2xy+y)
=-x²-2xy-y²+3-x²+2xy-y
=(-x²-x²)+(2xy-2xy)-y²-y+3
=-2x²-y²-y+3