x^2+y^2=x^2*y^2
(x+y)^2=x^2+y^2+2xy=x^2*y^2+2xy
设x+y=k
k^2=x^2y^2+2xy《((x+y)/2)^4+2((x+y)/2)^2=k^4/16+k^2/2
k^2》8
应该是最小值吧……
最小值是根8