Final answer:
Option B (3, 9, 27, 81, ...) is not an arithmetic sequence; it is a geometric sequence because the ratio between consecutive terms is a constant multiplier of 3. All other options are arithmetic sequences with a constant difference between terms.
Step-by-step explanation:
An arithmetic sequence is a sequence of numbers with a constant difference between consecutive terms. Let's examine each option to determine which one is not an arithmetic sequence:
- A) 1, 2, 3, 4, 5, ...: This is an arithmetic sequence because the difference between each term is consistently 1.
- B) 3, 9, 27, 81, ...: This is not an arithmetic sequence; it's actually a geometric sequence because each term is multiplied by 3 to obtain the next term (common ratio is 3).
- C) 4.5, 5.0, 5.5, 6.0, ...: This is an arithmetic sequence with a common difference of 0.5.
- D) 13, 2, -9, -20, -31 ...: This is an arithmetic sequence with a common difference of -11.
Therefore, the sequence that is not arithmetic is Option B, which is a geometric sequence.