Question

Помогите!!! Даю 55 баллов
Решить третий номер,
а б в

Answer 1

$b1 = 12 \ d = - 3 \ \ 1)bn = - 6 \ bn = b1 + d(n - 1) \ - 6= 12 - 3(n - 1) \ 15 - 3n = - 6 \ - 3n = - 21 \ n = 7 \ \ 2)bn = 0 \ 15 - 3n = 0 \ - 3n = - 15 \ n = 5 \ \ 3)bn = 9 \ 15 - 3n = 9 \ - 3n = - 6 \ n = 2$