Sum of Arithmetic Series

Adding a sequence of numbers where each number increases by the same amount.

Formula: Sₙ = n × (a₁ + aₙ) ÷ 2

1) sum of the first 5 terms of 2, 5, 8, 11, 14.

2) sum of the first 10 terms of 3, 7, 11, 15, ...