Question

Find the sum of the first nine terms 100,−40,16

Answer 1

9514 1404 393

Answer:

71.447296

Explanation:

The sequence is geometric with first term 100 and common ratio -0.4. Then the sum of n terms is ...

Sn = 100(1 -(-0.4)^n)/(1 -(-0.4))

and the sum of 9 terms is ...

S9 = 100(1 -(-0.4^9))/(1.4) = 71.447296