Question

Which of the following choices is the explicit formula for the following geometric sequence?

-0.1, 0.02, -0.004, 0.0008, -0.00016

A. an = 0.1(0.2)n
B. an = 0.1(-0.2)n-1
C. an = -0.1(-0.2)n-1
D. an = 0.2(-0.2)n-1
E. an = -0.1(0.2)n-1

Answer 1

i think it's C but im not sure

Explanation:

Answer 2

common ratio (r) can be found by dividing the second term by the first term.
0.02 / -0.1 = -0.2

an = a1 * r ^ (n - 1)
a1 = first term = -0.1
r = common ratio = -0.2

an = -0.1(-0.2)^(n - 1)...answer is C