Răspuns:
-4 sau 4
Explicație pas cu pas:
[tex]b_2=8,~\dfrac{b_1}{b_5}=\dfrac{1}{16},~=>~\dfrac{b_1}{b_1*q^4}=\dfrac{1}{16},~=>~\dfrac{1}{q^4}=\dfrac{1}{16},~=>~q^4=16,~=>~q=-2~sau~q=2.\\ b_2=b_1*q=8,~=>~b_1*(-2)=8,~=>~b_1=-4~sau~~b_1*2=8,~=>~b_1=4.\\[/tex]
