x>0,y>0
则x+y≥2√xy
所以xy≤(x+y)²/4
xy-(x+y)=1
xy=x+y+1≤(x+y)²/4
令a=x+y
a+1≤a²/4
a²-4a-4≥0
a≤2-2√2,a≥2+2√2
显然a＞0
所以a≥2+2√2
所以x+y最小值=2+2√2