- A geometric sequence has first term \(a\) and common ratio \(r\), where \(r > 0\)
Given that
- the 3rd term is 20
- the 5th term is 12.8
- show that \(r = 0.8\)
- Hence find the value of \(a\).
Given that the sum of the first \(n\) terms of this sequence is greater than 156
find the smallest possible value of \(n\).
(Solutions based entirely on graphical or numerical methods are not acceptable.)