Question

Ajuda em P. A!!!!!!!!!!!! (foto)

Answer 1

$a_{3} = a_{1} + 2r$
$a_{5} = a_{1} + 4r$
$a_{2} = a_{1} + r$

$\left \{ {{3 a_{1} + a_{1} + 2r =-12} \atop {5a_{1} + 4r+a_{1} + r=20}} \right.$

$\left \{ {{4 a_{1} + 2r = -12(/2)} \atop {6a_{1} + 5r=20}} \right.$

$\left \{ {{2 a_{1}+ r =-6} \atop {6a_{1} + 5r=20}} \right.$

1⇒ $r = -6 - 2 a_{1}$

2⇒ $6 a_{1} + 5(-6 - 2 a_{1})=20$
$6 a_{1} - 30 -10 a_{1} =20$
$-4 a_{1} =20+30$
$a_{1} = \frac{50}{-4}$
$a_{1} = -12,5$

1⇒ $r=-6-2(-12,5)$
$r=-6+25$
$r=19$

$P.A. = (-12,5; -6,5; 25,5; 44,5; ... )$