Question

Calcular o 6 termo da PG ( -9,-27.....)

Quantos termos tem a PG em que AN: 1875 A1: 3 Q: 5

calcular a soma dos termos da PG (5,20,......,1280)

Answer 1

q=a2/a1
q=-27/-9
q=3
an=a1.q^(n-1)
a6=-9.3^(6-1)
a6=-9.3^5
a6=-9.243
a6=-2187

an=a1.q^(n-1)
1875=3.5^(n-1)
625=5^(n-1)
5^4=5^(n-1)
4=n-1
n=4+1
n=5

Sn=a1. [q^n     -1]: [q-1]
vamos calcular "n" e "q"
q=a2/a1
q=20/5
q=4
1280=5.4^(n-1)
256=4^(n-1)
4^4=4^(n-1)
4=n-1
n=4+1
n=5

Sn=5[ 4^5    -1]:[4-1]
Sn=5[1024-1]:3
Sn=5[1023]:3
Sn=5*341
Sn=1705