Tentukan jumlah 15 suku deret geometri 3+9+27

Matematika
Barisan dan deret IX SMP

Pembahasan :
3 + 9 + 27 + ...

Rasio = U2/U1
Rasio = 9/3
Rasio = 3

Sn = a(rⁿ - 1)/(r - 1)
S15 = 3(3¹⁵ - 1)/(3 - 1)
S15 = 3(3¹⁵ - 1)/2
S15 = 21.523.359

Barisan dan Deret.

[tex]\displaystyle 3+9+27+...=\sum_{i=1}^{n}3^i=\frac{3}{2}\left ( 3^n-1 \right )\\ [/tex]
S₁₅ = 3/2 (3¹⁵ - 1)
       = 21523359