Question

For the following geometric sequence, find the recursive formula.
(-80, 20, -5, ...)

Answer 1

9514 1404 393

Answer:

• a[1] = -80
• a[n] = -a[n-1]/4

Explanation:

The first term is -80, so the first part of the recursive definition is ...

a[1] = -80

The common ratio is 20/-80 = -1/4, so the recursive rule is ...

a[n] = (-1/4)a[n-1]