Question

Даю балы на халяву
помогите пожалуйста!
спамерам бан​

Answer 1

$3)b_{1} =2\\\\b_{2}=6\\\\b_{2}=b_{1}*q\\\\q=\frac{b_{2}}{b_{1}}=\frac{6}{2}=3\\\\b_{8}=b_{1}*q^{7}=2*3^{7}=4374\\\\\boxed{b_{8}=4374}\\\\\\S_{7} =\frac{b_{1}(q^{7} -1)}{q-1}=\frac{2*(3^{7}-1) }{3-1}=2187-1=2186\\\\\boxed{S_{7}=2186}$

$4)b_{1} =9\\\\b_{2}=3\\\\b_{2}=b_{1}*q\\\\q=\frac{b_{2} }{b_{1} }=\frac{3}{9}=\frac{1}{3} \\\\S=\frac{b_{1} }{1-q}=\frac{9}{1-\frac{1}{3} }=\frac{9}{\frac{2}{3} }=\frac{9*3}{2}=13,5\\\\\boxed{S=13,5}$