S_{n} = \frac{n}{2} \cdot (a_{1} + a_{1} + (n - 1) \cdot d)

${S_n = \frac {n} {2} \cdot (a_1 + a_1 + (n -1) \cdot d)}$

S_{n} = \frac{n}{2} \cdot (a_{1} + a_{1} + (n - 1) \cdot d)

$S_n = \frac {n} {2} \cdot (a_1 + a_1 + (n -1) \cdot d)$

S_{n}

$S_n$

n

$n$

n

$n$

a_{1}

$a_1$

d

$d$