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已知数列{an}的前n项的和为Sn=1-1/(n+2),则a5+a6的值为
人气:460 ℃ 时间:2020-10-01 18:35:36
解答
Sn=1-1/(n+2)
S6 = 1-1/8 = 7/8
S4 = 1-1/6 = 5/6
a5+a6 = S6-S4 = 7/8 -5/6 = 1/24
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