一：一艘轮船从甲地逆流航行至乙地... 设距离为S，静水中速度为v，则：s/(v+3)=3/4*s/(v-3)解得v=21原式=1/x-1/(x+1)+1/(x+1)-1/(x+2)+...+1/1/(x+2004)-1/(x+2005)=...