Contoh 01

Tentukan nilai dari:

5 + 15 + 45 + ...

$r={\displaystyle \frac{15}{5}}=3$

Karena  $|r|\ge 1$ maka $S_{\sim }=\sim$

Contoh 02

Tentukan nilai dari:

27 + 9 + 3 + ...

$a=27$ dan $r={\displaystyle \frac{9}{27}}={\displaystyle \frac{1}{3}}$

Karena Karena  $|r|\le 1$ maka $S_{\sim }={\displaystyle \frac{a}{1-r}}$

$$\begin{array}{rl}{S}_{\sim }& =\frac{a}{1-r}\\ \\ S_{\sim }& =\frac{27}{1-\frac{1}{3}}\\ \\ S_{\sim }& =\frac{27}{\frac{2}{3}}\\ \\ S_{\sim }& =40\frac{1}{2}\end{array}$$