tolong dong, jawab nomer 1-2 pake cara, trimakasih ❤❤,please bantu aku yah

Penyelesaian:

1. U6 = 1215   = a.r^5
U4 = 135  = a.r^3

ar^3 . r^2 = 1215
r^2 = 1215 / 135
r^2 = 9
r = 3  (nilai rasio)

a.r^3 = 135
a.27 = 135
a = 5  (nilai a / suku awal)

Un = a.r^n-1
Un = 5.3^n-1  (rumus Un)

U5 = a.r^5-1
= 5.3^4
= 5.81 
U5 = 405  (nilai U5)

2. U5 = 15 = a.r^4
U3 = 375 = a.r^2

ar^2 . r^2 = 15
r^2 = 15/375
r^2 = 1/75
r = 1/15 . √3  (nilai rasio)

a.r^2 = 375
a . 1/75 = 375
a = (375)(75)
a = 28, 125  (nilai a / suku awal)

Un = a.r^n-1
U4 = a.r^4-1
= 28,125 . (1/15 . √3) . (1/15 . √3) . (1/15 . √3) 
= (28,125/3,375) . (3√3)
= 5625/675 . 3√3
= 225/27 . 3√3
= 225/9 . √3