Question

1-Calcule a soma dos termos da PG (4, 40,..., 40000000).

2-Calcule a soma dos termos da P.G. (4, 1,...).

Me ajudem!!
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Answer 1

Resposta:

1)

PG (4, 40,..., 40000000)

q=40/4=10

an=a1*q^(n-1)

40000000 =4 * 10^(n-1)

10000000 = 10^(n-1)

10^7=10^(n-1)

n-1=7  ==>n=8

Sn=a1*(1-q^n)/(1-q)

Sn=4 *(1-4^8)/(1-4) =  (4/3) *(4^8-1)

2)

q=a2/a1=1/4    ...para    -1 < q < 2 ==>Sn=a1/(1-q)

Sn=a1/(1-q)= 4/(1-1/4) =16/3