# Thread: Recursion and finding terms

1. ## Recursion and finding terms

I need to find the first 5 terms of a recursive formula. I don't have either the formula nor the terms, but I have 4 numbers: 3.5, -7, 14, -28.

How do I get the first 5 terms of it? How would I put it in terms of an = bn + c (or an+1, and so fourth)?

2. Originally Posted by Ramstien
I need to find the first 5 terms of a recursive formula. I don't have either the formula nor the terms, but I have 4 numbers: 3.5, -7, 14, -28.

How do I get the first 5 terms of it? How would I put it in terms of an = bn + c (or an+1, and so fourth)?
There's probably an expected answer that relies on you noticing that each term is obtained from the one before it by multiplying by -2. Hmmmmmm geometric series, a = 3.5, r = -2 ....... hmmmmmmm .........