Diketahui derek geometri suku pertama 6 dan suku ke4,48 jumlah 6 suku pertama adalah

a = 6

U4 = 48
a x r³ = 48
6 x r³ = 48
r³ = 8
r = 2

S6 = a (r pangkat n - 1) / (r - 1)
S6 = 6 (2 pangkat 6 - 1) / (2 - 1)
S6 = 6 (64 - 1) = 6 (63) = 378

#semoga membantu

U1 = a = 6
U4 = 48

Cara asli

U1/U4 = a × r^n - 1/ a × r^n - 1
6/48 = r^1 - 1 / r^4-1
1/8 = r^0 / r^3
1/2^3 = 1/r^3
2^-3 = r^-3
r = 2

Cara mudah

U4 = a × r^4-1
48 = 6 × r^3
48 ÷ 6 = r^3
8 = r^3
akar pangkat 3 dari 8 = r
akar pangkat 3 dari 2^3 = r
2 = r

Masuk ke rumus Sn

S6 = a (r^n - 1) / (r - 1)
= 6 (2^6 - 1) / (2-1)
= 6 (64 - 1) / 1
= 6 (63)
= 378

Semoga bermanfaat ^_^

Catatan :
r > 1 = a (r^n - 1 ) / (r - 1)
r < 1 = a (1 - r^n ) / (1 - r)