Question

已知正项等比数列{an}中,a1*a17=a11=16,求an.

Answer 1

a1*a17=a9^2=16

所以a9=4

又a11=16,a11=a9*q^2

d^2=a11/a9=4

q=2

所以

an=a9*q^(n-9)=4*2^(n-9)=2^(n-7)