楼上全错,正确的如下：已知x²+y²=4,求2xy/(x+y-2)的最小值.由于(x-y)²≥0,展开得：2xy≤x²+y²,则有：x²+y²+2xy≤2(x²+y²)(x+y)²≤2(x²+y²)=8得：-2√2...