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问题: 1×1/5+5*1/9+9*1/13+....+2004*1/2009=?

这题目的详细做法??小弟10分奉上

解答:



=(1/4)(1/5-1/9)+(1/4)(1/9-1/13)+...+(1/4)(1/2005-1/2009)
=(1/4)(1/5-1/9+1/9-1/13+...+1/2005-1/2009)
=(1/4)(1/5-1/2009)
=(1/4)×(2004/10045)
=501/10045