答：
共有100-1=99项,所有负号提取出来后乘积还是负数
(-1-1/2)*(-1-1/3)*(-1-1/4)*.*(-1-1/100)
=-(1+1/2)*(1+1/3)*(1+1/4).(1+1/100)
=-(3/2)*(4/3)*(5/4)*.*(101/100)
=-101/2