Question

Помогитеее с полным решением!!!!

Answer 1

$21)b_{1}= -3\\\\b_{2}=-\frac{3}{2}\\\\q=b_{2}:b_{1}=-\frac{3}{2}:(-3)=\frac{3}{2}*\frac{1}{3}=\frac{1}{2}\\S_{5}=\frac{b_{1}(q^{5}-1)}{q-1}=\frac{-3[(\frac{1}{2})^{5}-1]}{\frac{1}{2}-1 }=\frac{-3(\frac{1}{32}-1) }{-\frac{1}{2}}=6*(-\frac{31}{32})=-\frac{93}{16} =-5\frac{13}{16}\\\\\boxed{S_{5} =-5\frac{13}{16}}$

$22)a_{1} =2m+5\\\\a_{2} =m\\\\a_{3}=3m-8\\\\a_{2}=\frac{a_{1} +a_{3} }{2}\\\\m=\frac{2m+5+3m-8}{2}\\\\m=\frac{5m-3}{2} \\\\2m=5m-3\\\\3m =3\\\\\boxed{m=1}$