diketahui barisan geometri 1,3,9,27... jika un=2187 tentukan n

a = u₁
= 1

r = uₙ/uₙ ₋ ₁
= u₃/u₃ ₋ ₁
= u₃/u₂
= 9/3
= 3

uₙ = a × rⁿ ⁻ ¹
2.187 = 1 × 3ⁿ ⁻ ¹
2.187 = 3ⁿ/3¹
2.187 = 3ⁿ/3
3ⁿ = 2.187 × 3
3ⁿ = 6.561
3ⁿ = 3⁸
n = 8