The given arithmetic sequence is 7, 5, 3, 1, −1, ...
To find the recursive formula, we first identify the first term and the common difference.
- The first term \( a_1 = 7 \).
- The common difference \( d \) can be found by subtracting any term from the next term:
- \( 5 - 7 = -2 \)
- \( 3 - 5 = -2 \)
- \( 1 - 3 = -2 \)
- \( -1 - 1 = -2 \)
Thus, the common difference \( d = -2 \).
The recursive formula for an arithmetic sequence is generally expressed as:
\[ a_1 = \text{first term}, \quad a_n = a_{n-1} + d \]
In this case, we can set the recursive formula as follows:
\[ a_1 = 7, \quad a_n = a_{n-1} - 2 \]
Therefore, the correct response is:
a1=7, an=an−1−2