$a_1$ = First term

$a_n$ = N^th term

$d$ = Common difference

$n$ = No.of terms in the series

$S_n$ = Sum of n terms

• $a_n=a_1+(n-1)d $
• $S_n =\dfrac{n}{2}\left[\ 2a_1+(n-1)d \ \right] $
• $ S_n=\dfrac{n(a_1+a_n)}{2} $