这个题其实不难的,你可以直接带进去,y^2=x*z,2*a=x+y,2*b=y+z,x/a+z/b=2x/(x+y)+2z/(y+z)=2*[0x(y+z)+z(x+y)]/(x+y)*(y+z)=2(xy+2y^2+yz)/(xy+2y^2+yz)=2