=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