Question

Diketahui barisan geometri 15, 45, 105, ...., 3645. banyaknya suku bilangan pada barisan tersebut adalah ...

Answer 1

U2 = 15 x r^(2-1) = 45
r = 45/15 = 3

Un = 15 x 3^(n-1) = 3645
3^(n-1) = 243
3^(n-1) = 3^5
n-1 = 5
n = 5+1 = 6

Answer 2

Barisan Geometri
Un = ar^n-1
a= 15
b = 45/15 =3
3645 = 15 x 3^n-1
3645/15 = 3^n-1
243 = 3^n-1
karena 243 = 3^5
maka n -1 = 5
n = 5 + 1
n = 6 (banyak suku)