{an}为等比数列,公比r>1.a1+a2+a3=21及a1a2a3=216.(a)求通项an.用(a)结果求a1^a1a2^a2...an^an,n=1,2...

题目

{an}为等比数列,公比r>1.a1+a2+a3=21及a1a2a3=216.(a)求通项an.用(a)结果求a1^a1a2^a2...an^an,n=1,2...

答案

a1a2a3=216 a2=6
a1+a2+a3=21 6/q+6+6q=21 r=2
an=3.2(n-1)
(2) 3.(2(n-1+n-2+n-3+.1)=3.2(n^2/2)