已知数列{a(n)}满足a(1)=3 a(n)=(2n-1)/3^n (n>1)求s(n)

问题描述:

已知数列{a(n)}满足a(1)=3 a(n)=(2n-1)/3^n (n>1)求s(n)

Sn=a1+a2+a3+a4+.+anSn=3 + 3 / 3^2 + 5 / 3^3 + 7 / 3^4 +.+ (2n-1) / 3^n-------(1)两边同时除以 3 得1/3 Sn = 1 + 3 / 3^3 + 5 / 3^4 + 7 / 3^5 +.+ (2n-1) / 3^(n+1)----(2)(1)-(2)得2/3 ...