赞 endlesstory 幼苗
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1/(1*2) + 1/(2*3) + 1/(3 *4) + ...+ 1/(2008 * 2009)
= (1-1/2) +(1/2 - 1/3) + (1/3 - 1/4) + ...+ (1/2008- 1/2009)
= (1 - 1/2010)
= 2008/2009
= (1-1/2) +(1/2 - 1/3) + (1/3 - 1/4) + ...+ (1/2008- 1/2009)
= (1 - 1/2010)
= 2008/2009
1年前
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你能帮帮他们吗