my name is kabir and I am studying XI science I want to formulae of arithmetic progression.
$\displaystyle \displaystyle \begin{align*} t_n = a + (n-1)d \end{align*} $ and $\displaystyle \displaystyle \begin{align*} S_n = \frac{n}{2}[2a + (n-1)d] \end{align*} $ or $\displaystyle \displaystyle \begin{align*} S_n = \frac{n}{2}( a + l ) \end{align*} $.