Question

escreva a P.A  em que o quarto termo vale 24 e o nono termo vale 79

Answer 1

$a4=24\\a9=79\\an=a1+(n-1).r\\24=a1+3.r\\79=a1+8r\\\\ \left \{ {{24=a1+3.r}} \atop {79=a1+8r}} \right. \\\\24-79=3r-8r\\-55=-5r\\\\r=11\\\\\24=a1+3.11\\a1=24-33=-9\\\\a2=-9+11=2$

$\boxed{(-9,2,13,24,...)}$

Answer 2

Boa tarde!

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Dados:

a4→ 24

a9 → 79

n→ 9

r → ?

an → 79

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Em busca da razão da p.a :

An=a1+(n-1)·r → Formula da P.A

79=a4+(9-4)·r → reescrita

79=24+5r

79-24=5r

55=5r

r=55/5

r=11

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Em busca do a1:

An=a1+(n-1)·r

79=a1+(9-1)·11

79=a1+8·11

79=a1+88

79-88=a1

a1=-9

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P.A (-9, 2, 13, 24, 35, 46, 57, 68, 79)

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Att;Guilherme Lima