Question

Алгебра....
расписать
...

Answer 1

$b_1 = 11, \ b_4 = 88\\\\ \frac{b_4}{b_1} = q^3, \ \frac{88}{11} = 8 = 2^3 = q^3, \ q = 2\\\\ S_n = b_1 + ... + b_n = b_1 + b_1*q + ... + b_1*q^{n - 1} =\\\\ =b_1(1 + q + ... + q^{n - 1}) = b_1(\frac{q^n - 1}{q - 1})\\\\ S_5 = 11\frac{2^5 - 1}{2 - 1}= 11(32-1) = 11*31 = \boxed{341}$