(x+y)^2-(x-y)^2=(5√3)^2-(2√5)^2=75-20=55(x+y)^2-(x-y)^2=4xy∴4xy=55 xy=55/4 √(xy)=√(55/4)=(√55)/2求采纳呀求采纳
两式分别平方，展开，上式减下式得 xy=55/4 ,开根号得（根号下55）/2
失误
