已知数列『a.n』的前n项和为Sn,Sn=3n-2.(三的n次方减二!)求a.n

问题描述:

已知数列『a.n』的前n项和为Sn,Sn=3n-2.(三的n次方减二!)求a.n

a.n = Sn - S(n-1) = (3^n -2) - (3^(n-1)-2) = 2*3^(n-1)