Question

Which of the following is a geometric sequence?

A. 2, –2, 2, –2, 2, –2, ...

B. 5, 3, 1, –1, –3, ...

C. 1, 2, 4, 6, 8, 10, ...

D. –1, 0, 1, 2, 3, ...

Answer 1

B its show you the sequence following

Answer 2

Answer: Choice A

Reason:

The common ratio is -1. We can determine this by dividing each term over its previous term.

• r = common ratio
• r = term2/term1 = -2/2 = -1
• r = term3/term2 = 2/(-2) = -1
• r = term4/term3 = -2/2 = -1

and so on.

This means we multiply each term by -1 to get the next term.

Choice B is not geometric because term2/term1 = 3/5 = 0.6 and term3/term2 = 1/3 = 0.33 approximately. We don't get the same result after dividing. Choices C and D are a similar story.