Arithmetic progression
Sequences, series and the binomial theorem · Mathematics
Study notes
Q: Identify the AP and find d: 5, 8, 11, 14, ... Find the sum of the first 20 terms. Step 1: Differences: 8-5 = 3, 11-8 = 3. Constant, so AP with a = 5, d = 3. Step 2: S₂₀ = 20/2·(2(5) + 19(3)) = 10·(10 + 57) = 10 × 67 = 670.