Question

Дано q=2 S4=189 Найти b1=?

Answer 1

$S_{n} = frac{b_{1}(q^{n}-1)}{q-1}$
$n =4$
$q =2$
$S_{4} = frac{b_{1}(q^{4}-1)}{q-1}$
$189 = frac{b_{1}(2^{4}-1)}{2-1}$
$189= b_{1}*15$
$b_{1}= frac{189}{15}$
$b_{1}= 12,6$