[tex]P.A(a_{1},a_{2},a_{3},a_{4},a_{5})[/tex]
[tex]S_{5} = S_{i}[/tex]
[tex](a_{1} + a_{5})*5/2 = (n - 2)*180^{0}[/tex]
[tex](a_{1}+a_{1}+4r)*5/2=(5 - 2)*180^{0}[/tex]
[tex](2a_{1}+4r)*5/2=3*180^{0}[/tex]
[tex]2(a_{1}+2r)*5/2=540^{0}[/tex]
[tex]a_{1}+2r=540^{0}/5[/tex]
[tex]a_{1}+2r=108^{0}[/tex]
Sabemos que [tex]a_{3} = a_{1} + 2r[/tex]
[tex]a_{3}=108^{0}[/tex]
Letra B)