S_{n} = a_{1} \cdot \frac{q^{n} - 1}{q - 1}

${S_n = a_1 \cdot \frac {q^n - 1} {q - 1}}$

S_{n} = a_{1} \cdot \frac{q^{n} - 1}{q - 1}

$S_n = a_1 \cdot \frac {q^n - 1} {q - 1}$

S_{n}

$S_n$

a_{1}

$a_1$

a_{1}

$a_1$

1

q

$q$

1

n

$n$

1

Lisa