两式相加x²+3xy+xy+4y²=28+8（x+2y）²=36x+2y=±6x=6-2y 或x=-6-2yxy+y²=8y(x+y)=8x=6-2y时y(6-2y+y)=8y(6-y)=8y²-6y+8=0(y-4)(y-2)=0y1=4 y2=2x1=-2 x2=2x=-6-2y时y(-6-2y+y)=8y(-6-y)=8y...