Pada deret geometri diketahui U2 = 24 dan U5 = 648. Jumlah rumus n suku pertama adalah... a. Sn = 2(5n - 1) b. Sn = 4(4n) c. Sn = 1/2(3n-1) d. Sn = 3(4n-1) e. Sn = 4(3n-1)
subebe
U5/U2 = ar^4/ar r^3 = 648/24 r^3 = 27 r = 3 U2 = ar 24 = a(3) 3a = 24 a = 8 Sn = a(r^n - 1)/(r-1) = 8(3^n - 1)/ 2 Sn = 4 (3^n - 1)
r^3 = 648/24
r^3 = 27
r = 3
U2 = ar
24 = a(3)
3a = 24
a = 8
Sn = a(r^n - 1)/(r-1)
= 8(3^n - 1)/ 2
Sn = 4 (3^n - 1)