suku ke 4 = 54 dan suku ke 7 = 2. tentukan jumlah suku ke 9

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

r = ⁷⁻⁴√(U7 : U4)
r = ∛(2/54)
r = ∛(1/27)
r = 1/3

a = U4 : r³
a = 54 : (1/3)³
a = 54 : 1/27
a = 54 . 27
a = 1.458

Sn = a . (1 - rⁿ)/(1 - r)
S9 = 1.458 . (1 - (1/3)⁹) / (3/3 - 1/3)
S9 = 1.458 . (19.683/19.683 - 1/19.683) / (2/3)
S9 = 1.458 . (19.682/19.683) . (3/2)
S9 = 19.682/9
S9 = 2.186 8/9