Question

escreva uma pa de 9 termos sendo que A3=5 e R=-4

Answer 1

vamos lá...

achar o a₁

an=a₃=5        n=3     r=-4

an=a₁+(n-1)r
5=a₁+(3-1)(-4)
5=a₁+(2)(-4)
5=a₁-8
5+8=a₁
a₁=13

veja
a₁=13
a₂=a₁+r=13-4=9
a₃=a₁+2r=13+2(-4)=13-8=5
a₄=a₁+3r=13+3(-4)=13-12=1
a₅=a₁+4r=13+4(-4)=13-16=-3
a₆=a₁+5r=13+5(-4)=13-20=-7
a₇=a₁+6r=13+6(-4)=13-24=-11
a₈=a₁+7r=13+7(-4)=13-28=-15
a₉=a₁+8r=13+8(-4)=13-32=-19

P.A (13,9,5,1,-3,-7,-11,-15,-19)