Sum of a GP
Sequences, series and the binomial theorem · Mathematics
Study notes
Q: Find the sum of the first 10 terms of 2, 6, 18, ... Step 1: a = 2, r = 3, n = 10. Step 2: S₁₀ = 2(3¹⁰ - 1)/(3 - 1) = 2(59049 - 1)/2 = 59048. Step 3: Check small: S₃ = 2 + 6 + 18 = 26. Formula: 2(27-1)/2 = 26 ✓.