Write a rule for the nth term of the sequence: 5, 15, 45, 135, ...

Question

a) a_n = 10n-5

b) a_n = 10n+5

c) a_n = 5(-3)^n-1

^d) a_n = 5(3)^n-1

Answer 1

Hi Georgia,

This is a geometric sequence and the ratio is 3. i divided 15 by 5 and got 3. We can do the same thing for the other terms divide a term by its preceding term.

We have the first term 5

We have the ratio which is 3

the formula is represented by letter d. first term multiplied by the ratio raised to the number of terms less 1 because we have accounted for the first term.