Question

Find the nth term of this number sequence

15, 12, 9, 6, ...

Answer 1

`a_(n)` = 18 - 3n

Explanation:

there is a common difference between consecutive terms in the sequence, that is

12 - 15 = 9 - 12 = 6 - 9 = - 3

this indicates the sequence is arithmetic with nth term

`a_(n)` = a₁ + (n - 1)d

where a₁ is the first term and d the common difference

here a₁ = 15 and d = - 3 , then

`a_(n)` = 15 - 3(n - 1) = 15 - 3n + 3 = 18 - 3n