The common difference of the arithmetic sequence 21, 15, 9 is -6.
Here's how we find the common difference in an arithmetic sequence:
- An arithmetic sequence is a series of numbers where the difference between any two consecutive terms is constant. This constant difference is known as the common difference, often denoted by the letter 'd'.
- To calculate the common difference, you subtract any term from the term that immediately follows it.
- Let's verify using the sequence 21, 15, 9:
- Subtract the second term from the first term: 15 - 21 = -6
- Subtract the third term from the second term: 9 - 15 = -6
- As indicated in the reference, $d = 15 - 21 = 9 - 15 = -6$. This consistent difference (-6) confirms that the sequence is an arithmetic sequence and that the common difference is -6. Note that the reference contained an incorrect common difference.
Therefore, the common difference of the arithmetic sequence 21, 15, 9 is -6.
