Question

помогите пожалуйста, хотя бы 1 задание​

Answer 1

$6)a_{1}=-8\\q=3\\ S_{n}=-2912\\\\S_{n}=\frac{a_{1}(q^{n}-1)}{q-1}\\\\-2912=\frac{-8*(3^{n}-1) }{3-1}\\\\-2912=-4(3^{n} -1)\\\\3^{n}-1=728\\\\3^{n}=729\\\\3^{n}=3^{6} \\\\n=6\\\\Otvet:\boxed{n=6}$

$7)\left \{ {{b_{4}-b_{2}=30} \atop {b_{4}-b_{3}=24}} \right.\\\\\left \{ {{b_{1}*q^{3}-b_{1}*q=30} \atop {b_{1}*q^{3}-b_{1}*q^{2}=24}} \right.\\\\:\left \{ {{b_{1}q(q^{2}-1)=30} \atop {b_{1}q^{2}(q-1)=24}} \right. \\-------\\\frac{q}{q+1}=\frac{4}{5}\\\\5q=4q+4\\\\q=4\\\\b_{1}=\frac{24}{q^{2}(q-1)}=\frac{24}{4^{2}(4-1)}=\frac{24}{16*3}=\frac{1}{2}=0,5\\\\S_{5}=\frac{b_{1}*(q^{5}-1)}{q-1}=\frac{0,5*(4^{5}-1)}{4-1}=\frac{0,5*(1024-1)}{3}=\frac{0,5*1023}{3}=0,5*341=170,5$