1）条件导出y-x=2xy,再代入到式子里,变成-5xy/-3xy=5/3
2) x(x+1)=1, 设定y=x(x+1),x4+x2+2x-1=x4+2x3+x2-2x3-2x2+2x2+2x-1=y2-2xy+2y-1=3-根号5字母后面紧跟的数字是方次.
恩,加了补充就利索多了