Rumus suku ke-n barisan geometri 9, 27, 81, 243, ... adalah ....

9,27,81,243,...
a = 9
r = U2 / a = 27 / 9 = 3
Un = a × r (n - 1)
= 9 × 3 (n - 1)
= 3.2 × 3 (n - 1)
= 3 (2 + n - 1)
= 3 (n + 3).