=x1-x2+2(1/x1-1/x2) =(x1-x2)+2(x2-x1)/x1x2 =(x1-x2)-2(x1-x2)/x1x2 =(x1-x2)(1-2/x1x2) =(x1-x2)(x1x2-2)/x1x2 根据其他条件，分别判断x1-x2,x1x2-2和x1x2的符号，然后就可以知道是大于0还是小于0
