x大于0 ,y大于0,且(x-1)(y-1)大于等于2,x+y的范围

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x大于0 ,y大于0,且(x-1)(y-1)大于等于2,x+y的范围
x大于0 ,y大于0,且(x-1)(y-1)大于等于2,x+y的范围

x大于0 ,y大于0,且(x-1)(y-1)大于等于2,x+y的范围
(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<=-1