Question

Another sigma notation question. Please check. Hopefully I did this one correctly!

Answer 1

Your answer is correct. The series is a geometric series with common ratio -1/4 and first term 40. So each term is:

an = 40 (-1/4)^(n−1)

So the sum of the first 10 terms is:

∑(n=1 to 10) [ 40 (-1/4)^(n−1) ]