Resposta :
[tex]\boxed{\begin{array}{l}\sf a_5=a_1+4r\\\sf-6=-8+4r\\\sf 4r=8-6\\\sf 4r=2\\\sf r=\dfrac{2}{4}=0,5\\\sf a=-8+0,5=-7,5\\\sf b=-7,5+0,5=-7\\\sf c=-7+0,5=-6,5\end{array}}[/tex]
[tex]\boxed{\begin{array}{l}\sf a_5=a_1+4r\\\sf-6=-8+4r\\\sf 4r=8-6\\\sf 4r=2\\\sf r=\dfrac{2}{4}=0,5\\\sf a=-8+0,5=-7,5\\\sf b=-7,5+0,5=-7\\\sf c=-7+0,5=-6,5\end{array}}[/tex]