相同分子的分数,分母越小,分数值越大.又正数和零的绝对值为其本身,负数的绝对值为其相反数.所以原式=-(1/2001-1/2000)-(1/2002-1/2001)+(1/2002-1/2000)=-1/2001+1/2000-1/2002+1/2001+1/2002-1/2000=0