Question

The first term of a geometric sequence is -2 and the multiplier, or ratio, is -3. what is the sum of the first 5 terms of the sequence?

a. 162
b. 122
c. -122
d. -162

Answer 1

To determine the sum of the sequence, we can finfd the first five terms however it would be tedious. Instead, we can find the sum by the expression:

S(n) = a(1) ( 1 - r^n) / 1-r
S(5) = -2 (1 - (-3)^5) / 1-5
S(9) = 122 <------------OPTION B