baris geometri u4=54 u6=486.tentukan u7 dan s7

Bab Barisan dan Deret
Matematika SMP Kelas VIII

^ = pangkat

Geometri

1] r = (U6 : U4)^1/(6 - 4)
r = (486 : 54)^(1/2)
r = 9^(1/2)
r = 3

U7 = U6 x r
U7 = 486 x 3
U7 = 1.458

2] a = U4 : r^3
a = 54 : 3^3
a = 54 : 27
a = 2

Sn = (a x (r^n - 1)) / (r - 1)

S7 = (2 x (3^7 - 1)) / (3 - 1)
S7 = (2 x (2.187 - 1)) / 2
S7 = 2.186