Question

Given a_4=135\;and\;a_6=1215a

4
​
=135anda
6
​
=1215, find the explicit rule for the geometric sequence, given that the common ratio is positive.

Answer 1

Explanation:

let a be first term and r be c.r.

a_{n}=ar^{n-1}

a_{4}=ar^{4-1}=ar^3=135

a_{6}=ar^{6-1}=ar^5=1215a_{4}=1215 \times 135

divide

r^2=1215

r=√1215=35

a_{n}=35 a_{n-1}