Question

Геометрическая прогрессия.найти b1 и Sn если q=13 ,n=6 ,bn=581

Answer 1

b6 = b1*$q^{5}$ 

5/81 = b1 *  $/(1/3)^{5}$ 

5/81 = 1/243*b1

b1 = 15

Sn = $frac{bn*q - b1}{q -1}$

S6 =  $frac{5/81 * 1/3 - 15}{1/3 -1}$ = 1820/81