Sn=1/2^2+2/2^3+3/2^4+4/2^5+……+(n-1)/2^n+n/2^(n+1)2Sn=1/2+2/2^2+3/2^3+4/2^4+……+(n-1)/2^(n-1)+n/2^n两式相减：Sn=1/2+1/2^2+1/2^3+1/2^4+1/2^5+……+1/2^n-n/2^(n+1)=(1/2)[(1/2)^n-1]/(1/2-1)-n/2^(n+1)=1-...