Question

помогите пожалуйста, хотя бы 1 задание​

Answer 1

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

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