Question

b1=4 n=7 q=2 b3=? Sn=?

Answer 1

Ответ: b₃=16,  S₇=508.

Объяснение:

$\displaystyle\\b_1=4\ \ \ \ n=7\ \ \ \ q=2\ \ \ \ b_3=?\ \ \ \ S_7=?\\\\b_3=b_1q^2=4*2^2=4*4=16.\\\\S_7=4*\frac{2^7-1}{2-1}=4*\frac{128-1}{1} =4*127=508.$