令x1>x2>1f(x1)-f(x2)=x1+1/x1-x2-1/x2=(x1²x2+x2-x1x2²-x1)/x1x2分母x1x2>0分子=x1x2(x1-x2)-(x1-x2)=(x1x2-1)(x1-x2)x1>x2,所以x1-x2>0x1>1,x2>1,所以x1x2-1>0所以分子大于0所以x1>x2>1,f(x1)>f(x2)所以...