nth term of a GP
Sequences, series and the binomial theorem · Mathematics
Study notes
Q: Find the 8th term of 5, 10, 20, ... Which term is 640? Step 1: a = 5, r = 2. Step 2: T₈ = 5 × 2⁷ = 5 × 128 = 640. Step 3: 640 is the 8th term! (Also: 5·2^(n-1) = 640 → 2^(n-1) = 128 = 2⁷ → n = 8.)