1/[X+1] + 1/[Y+1]
=(y+1+x+1)/(x+1)(y+1)
=(4+2)/(xy+x+y+1)
=6/(xy+5)
x+y>=2√(xy)
xy=6/(4+5)=2/3
即:1/(x+1)+1/(1+y)的最小值是:2/3