Question

Given the sequence in the table below, determine the sigma notation of the sum for term 4 through term 15

Answer 1

@Directrix

Answer 2

Term
1 5 5 * 1 5 * (-2)^0
2 -10 5 * (-2) 5 * (-2)^1
3 20 5 * (-2) * (-2) 5 * (-2)^2

Notice that the exponent is 1 less than the term number, so it looks like this:
\(5(-2)^{n - 1} \)