Question

For the following geometric sequence find the recursive formula: {-1, 3, -9, ...}.

an = (-3) n - 1
an = -3 · an - 1 where a1 = -1
an = -3 · an - 1 where a1 = 1
an = -1 · (-3) n - 1

Answer 1

an = -3 · an - 1 where a1 = -1.

Explanation:

The first term a1 = -1 and the common ratio is -3 so ecah term is formed form the previous one by multiplying by -3.