已知x+y=5根号3,x-y=2根号5,则根号xy=
问题描述：
已知x+y=5根号3,x-y=2根号5,则根号xy=
答
(x+y)^2=x^2+2xy+y^2=75
(x-y)^2=x^2-2xy+y^2=20
两者相减：x^2+2xy+y^2-(x^2-2xy+y^2)=4xy=55
xy=55除4=13.75