Pada sebuah barisan geometri, diketahui bilangan ke-2 = 6 dan suku ke-4 = 54

Jawaban:

Un = ar^(n-1)

U2 = ar^(2-1) = 6

ar= 6

a = 6/r

U4 = ar^(4-1) = 54

ar³ = 54

6/r × r³ = 54

6r^-1 ×r³ = 54

6r² = 54

r² = 9

r = 3

ar = 6

a(3) = 6

a = 2

a. U6 = 2×3^(6-1)

= 2×3^5

= 2×243

= 486

b. Sn = a(r^n -1)/r-1

S6 = 2(3^6 -1)/3-1

= 2(729-1)/2

= 728