Question

which word best describes this formula for the sequence $a_n$?
$a_n = 4a_{n - 2} - 9a_{n - 3}$
explicit \t recursive

Explanation:

A recursive sequence formula defines a term using previous terms of the sequence. The given formula $a_n = 4a_{n-2} - 9a_{n-3}$ defines $a_n$ using earlier terms $a_{n-2}$ and $a_{n-3}$, which fits the definition of a recursive formula. An explicit formula would define $a_n$ directly in terms of $n$ without referencing prior sequence terms.

Answer:

recursive