$a_1$ = First term

$a_n$ = N^th term

$r$ = Common ratio

$n$ = No.of terms in the series

$S_\infty$ = Sum of infinite terms

• $a_n=ar^{n-1}$
• $S_n=\dfrac{a_1(r^n -1)}{r-1}$
• $S_\infty = \dfrac{a_1}{1-r}~(\text{for } -1 < r < 1)$