Question

Find the 12th term of the geometric sequence 5, 20, 80, ...5,20,80

Answer 1

a₁₂ = 20971520

Explanation:

The nth term of a geometric sequence is

`a_(n)` = a₁
`(r)^(n-1)`

where a₁ is the first term and r the common ratio

Here a₁ = 5 and r = a₂ ÷ a₁ = 20 ÷ 5 = 4 , then

a₁₂ = 5 ×
`4^(11)` = 5 × 4194304 = 20971520