Question

determine o vigésimo oitavo termo da PA = (5;3;1;-1;...)
a) -49 b)-67 c) +15 d)-36

Answer 1

Calcular a razão da PA

Razão  = a2 - a1
r = a2 - a1
r = 3 - 5
r = -2

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Calcular o valor do termo a28

an =   a1 + ( n -1 ) . r
a28 =  5 + ( 28 -1 ) . ( -2 )
a28 =  5 + ( 27 ) . -2
a28 =  5 - 54
a28 =  -49

Resposta letra a) -49

Answer 2

a1= 5
an=?
r= -2
n= 28
an= a1 + (n-1) *r
an= 5 + (28-1) *(-2)
an= 5 + 27 *(-2)
an= 5+ (-54)
an= -49
p.a.(5,3,1,-1,-3,-5,-7,-9,-11,-13,-15,-17,-19,-21,-23,-25,-27,-29,-31,-33,-35,-37,-39,-41,-43,-45,-47,-49)