The sequence 3, 5, 7, 9, ... is an arithmetic progression with:

- First term \(a_1 = 3\)
- Common difference \(d = 2\)

General \(k^{th}\) term:
\(a_k = 3 + (k-1) \cdot 2 = 2k + 1\)

For the \((n-2)^{th}\) term, substitute \(k = n-2\):
\(a_{n-2} = 2(n-2) + 1 = 2n - 4 + 1 = 2n - 3\)

The expression is \(2n - 3\)