Question

x大于0 ,y大于0,且（x-1)(y-1)大于等于2,x+y的范围

Answer 1

（x-1)(y-1)大于等于2

xy-x-y+1>=2

xy-x-y>=1

xy-1>=x+y

因为x>0,y>0

所以xy>0

xy-1>-1

x+y