Write the sum using sigma notation: − 3 − 6 − 12 + ... − 48 - 3 - 6 - 12 + ... - 48

Answer 1

First compare the index with the term. We can create a table of the indexes and their corresponding terms

n a_n

1 -3

2 -6

3 -12

4 -24

5 -48

Once we do that, we can find a general formula for each term

a_n = -3* 2^n-1

We're adding these terms from n = 1 to n = 5 so the sigma notation would be

5

∑ -3 * 2^k-1

k=1