六年级数学天天练试题及答案2019.1.17(分数列项)(2)
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2018-12-02 18:10:40
【答案】
1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+1/(4×5×6)+…+1/(21×22×23)
=(1/2)【1/(1×2)-1/(2×3)+1/(2×3)-1/(3×4)+1/(3×4)-1/(4×5)+1/(4×5)-1/(5×6)+…+1/(21×22)-1/(22×23)】
=(1/2)【1(1×2)-1/(22×23)】
=(1/2)(126/253)
=63/253
