若x大于0，y大于0且2x+8y-xy=0求x+y的最小值

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2x+8y=xy
2/y+8/x=1

x+y=(x+y)*1
=(x+y)(2/y+8/x)
=2x/扒大y+8y/x+2+8

x>0,y>0
2x/y+8y/x>丛此岁渗睁=2√(2x/y*8y/x)=8
所以x+y最小值=8+2+8=18

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