Which of these is a geometric sequence?
a. 2, 4, 6, 8, 10,
b. 3, 15, 75, 375, 1875,
c. 2,3,5,9,
d. 1/3,2,3,
apex

It's C.

Step-by-step explanation:

A geometric sequence has a common ratio (r) where each term after the first is obtained by multiplying the previous one by r.

Checking through the list we see it is C because:

Second term 15 = first term * 5 = 3(5) = 15.

Third term = 15*5 = 75,

4th term  = 75*5 = 375  and so on.

The common ratio is 5.

 Sequence C is a little different because it seems that we are dividing; yet to stay consistent with the theme of geometric sequences, we must think in terms of multiplication. We need to multiply by -1/2 to the first number to get the second number. This too works for any pair of consecutive numbers. The fourth number times -1/2 is the fifth number: -2 × -1/2 = 1.

- Martiinez <3

the correct is answer is a 9-sided polygon!