Sum of Geometric sequence. 1. find the sum of the first five terms of the geometric series 6, 12, 24 2. find the sum of the first seven terms of a geometric me whose first term is 3 and the common ratio 4 Sn = a₁c²³ first term sequence 1-->>> common ratio 3. find the sum of the terms of the geometric series if a₁ = 1 and v² =2 4. 2, 6, 18, 54, 162