hfq1999
幼苗
共回答了20个问题采纳率:80% 举报
Sn=(1/2)+(1/2)^2+(1/2)^3+...+(1/2)^n ...(1)
1/2Sn= (1/2)^2+(1/2)^3)+...+(1/2)^n+(1/2)^(n+1) ...(2)
(1)-(2):1/2Sn=(1/2)-(1/2)^(n+1)
Sn=1-(1/2)^n=1-1/2^n
1年前
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hfq1999
S=1/2+(1/2)^2+...+(1/2)^6 =2^5/2^6+2^4/2^6+...+1/2^6 =(2^5+2^4+2^3+2^2+2+1)/2^6 =(32+16+8+4+2+1)/64 =63/64