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