已知x,y满足x^2+y^2+5/4=2x+y,求代数式xy/(x+y)
x^2+y^2+5/4=2x+y
x^2-2x+1+y^2-y+1/4=0
(x-1)^2+(y-1/2)^2=0
x-1=0,x=1
y-1/2=0,y=1/2
xy/(x+y)=1/3