Question

b1=3,q=3,n=7,b3=?,Sn=?​

Answer 1

$S_{n} = \frac{b_{1}( {q}^{n} - 1)}{q - 1}$

$S_{7} = \frac{b_{1}( {q}^{7} - 1)}{q - 1} = \frac{3( {3}^{7} - 1)}{3 - 1} = 3279$

$b_{n} = b_{1} \times q {}^{n - 1}$

$b_{3} = b_{1} \times q {}^{2} = 3 \times 3 {}^{2} = 27$