y均为正数,且xy=2x+y-1,则x+y的最小值
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y均为正数,且xy=2x+y-1,则x+y的最小值
y均为正数,且xy=2x+y-1,则x+y的最小值
y均为正数,且xy=2x+y-1,则x+y的最小值
解由xy=2x+y-1
得(x-1)y=2x-1
即y=(2x-1)/(x-1)
故x+y
=x+(2x-1)/(x-1)
=[(x^2-x)+(2x-1)]/(x-1)
=(x^2+x-1)/(x-1)
=[(x-1)^2+3(x-1)+1]/(x-1)
=(x-1)+1/(x-1)+3
≥2√(x-1)*1/(x-1)+3
=5
当且仅当x=2时,等号成立
故x+y的最小值为5.