(1+x+2y)²=[(x+1)+(2y)]²=(x+1)²+(x+1)(2y)+(2y)²=x²+2x+1+2xy+2y+4y²=x²+2xy+4y²+2x+2y+1（2x-7y）（3x+4y-1）=2x(3x+4y-1)-7y(3x+4y-1)=(6x²+8xy-2x)-(21xy+28y...