Resposta:
Explicação passo a passo:
[tex]a_{8}=16[/tex]
[tex]a_{9}=20[/tex]
[tex]a_{5}=\:?[/tex]
[tex]\left\{\begin{array}{ccc}a_{1}+7r=16 \\\\a_{1}+8r=20 \end{array}\right[/tex]
[tex]\left\{\begin{array}{ccc}-a_{1}-7r=-16 \\\\a_{1}+8r=20 \end{array}\right[/tex]
[tex]r=4[/tex]
[tex]a_{1}+7r=16[/tex]
[tex]a_{1}+7.(4)=16[/tex]
[tex]a_{1}+28=16[/tex]
[tex]a_{1}=16-28[/tex]
[tex]a_{1}=-12[/tex]
[tex]a_{5}=a_{1}+4r[/tex]
[tex]a_{5}=-12+4.(4)[/tex]
[tex]a_{5}=-12+16[/tex]
[tex]a_{5}=4[/tex]
