两条对角线的长度x,yxy/2=120---------------------->xy=240.(1)(x/2)^2+(y/2)^2=(52/4)^2------>x^2+y^2=676...(2)(2)+2*(1):x^2+y^2+2xy=1156x+y=34.(3)(2)-2*(1):x^2+y^2-2xy=1156x-y=14.(4)两条对角线的长度(3)+...