suku ke 5 dan suku ke 2 dari barisan geometri masing-masing 162 dan 6, maka jumlah tiga suku pertama barisan tsb adalah...

U5-1 = ar^4 = 162
U2-1 = ar^1 = 6

ar^4 = 162
ar^1 = 6
--------------
r^3 = 27
r = 3

ar = 6
a x 3 = 6 → 3a = 6
a = 6 : 3 = 2
a = 2

S3 = a(r^3-1)

r-1
= 2(3^3 - 1)

3-1
= 2(27-1)

2
= 26

S3 = 26

Dik : U5 = 162
U2 = 6
Dit : S3=....?
penye
U5. 162
---- = ------
U2. 6

ar^5-1. 162
--------- = ------
ar^2-1. 6

ar^4. 162
------- = --------
ar. 6

r^3 = 27
r = 3

ar = 6
a(3) = 6
3a = 6
a = 6/3
a = 2

S3 = a(r^3 -1)
-------------
r-1
= 2(3^3 - 1)
--------------
3-1
= 2(27-1)
---------
2
= 26

Semoga Membantu.><