To derive a recursive formula for the sequence \( { a_n } = { 15, 26, 37, 48, 59, \ldots } \), we first observe that the difference between consecutive terms is constant.
Calculating the differences:
- \( a_2 - a_1 = 26 - 15 = 11 \)
- \( a_3 - a_2 = 37 - 26 = 11 \)
- \( a_4 - a_3 = 48 - 37 = 11 \)
- \( a_5 - a_4 = 59 - 48 = 11 \)
The common difference is \( 11 \). This indicates that the recursive formula can be constructed using this difference.
A suitable recursive formula for this sequence is:
\[ \begin{cases} a_1 = 15 \ a_n = a_{n-1} + 11 \quad \text{for } n > 1 \end{cases} \]
This formula states that the first term \( a_1 \) is 15, and each subsequent term \( a_n \) is obtained by adding 11 to the previous term \( a_{n-1} \).