S_n = \fracn2 \left(2a + (n - 1)d\right) = \fracn2 \left(2(7) + (n - 1)(4)\right) = \fracn2 (14 + 4n - 4) = \fracn2 (4n + 10) - AMAZONAWS

S_n Formula Explained: Mastering the $n$-th Term of an Arithmetic Sequence

📅 March 6, 2026 👤 scraface

Mar 06, 2026

$S_n = \frac{n}{2} \left(2a + (n - 1)d\right) = \frac{n}{2} \left(2(7) + (n - 1)(4)\right) = \frac{n}{2} (14 + 4n - 4) = \frac{n}{2} (4n + 10)$