deret geometri a=4 dan u5=324 ditanyakan s5=?

Barisan dan Deret Geometri.

Un = arⁿ⁻¹
ar⁴ = 324
r = (324 / 4)^(1/4) = 3

Sn = a(rⁿ - 1) / (r - 1)
S₅ = 4(3⁵ - 1) / (3 - 1)
     = 484

Cari rasio

[tex]$\begin{align}U_5&=ar^4\\324&=4r^4\\r&=\sqrt[4]{\frac{324}4}\\&=\sqrt[4]{81}\\&=3\end[/tex]

Maka, S₅ adalah

[tex]$\begin{align}S_n&=\frac{a\left(r^n-1\right)}{r-1}\\S_5&=\frac{4\left(3^5-1\right)}{3-1}\\&=\frac{4(242)}{2}\\&=\boxed{484}\end[/tex]