已知A=4X平方减4XY+Y平方,B=x平方+XY减5Y平方
(1) A+2B=4x²-4xy+y²+2(x²+xy-5y²)
=4x²-4xy+y²+2x²+2xy-10y²
=6x²-2xy-9y²
(2) 2A-B=2(4x²-4xy+y²)-(x²+xy-5y²)
=8x²-8xy+2y²-x²-xy+5y²
=7x²-9xy+7y²
(3) A-(2A+B)
=A-2A-B
=-A-B
=-(4x²-4xy+y²)-(x²+xy-5y²)
=-4x²+xy-y²-x²-xy+5y²
=-5x²+4y²