1/2Sn=1/2^2 + 1/2^3 + 1/2^n+1 - 1/2^n+2,然后Sn等于多少?
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1/2Sn=1/2^2 + 1/2^3 + 1/2^n+1 - 1/2^n+2,然后Sn等于多少?
左右两边×2
Sn=1/2^1 + 1/2^2 + 1/2^n - 1/2^(n+1)
等比数列求和
=(1/2-1/2^(n+1))/(1-1/2)-1/2^(n+1)
=1-1/2^n-1/2^(n+1)
=1-3/2^(n+1)
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再问: 答案是Sn=1-1/2^n - n/2^n l
再答: ����������Ŀ���� =1-1/2^n-1/2^(n+1) =1-3/2^(n+1) ��Ĵ
Sn=1/2^1 + 1/2^2 + 1/2^n - 1/2^(n+1)
等比数列求和
=(1/2-1/2^(n+1))/(1-1/2)-1/2^(n+1)
=1-1/2^n-1/2^(n+1)
=1-3/2^(n+1)
很高兴为您解答,【学习宝典】团队为您答题.
请点击下面的【选为满意回答】按钮,
再问: 答案是Sn=1-1/2^n - n/2^n l
再答: ����������Ŀ���� =1-1/2^n-1/2^(n+1) =1-3/2^(n+1) ��Ĵ
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