Question

Determine quantos termos tem a PG(5, 10, ..., 5120)

Answer 1

an = 5120
a1 = 5

q = a2 
       a1
q = 10
        5
q = 2

an= a1.q^n-1
5120=5.2^n-1
5120=2^n-1
   5
1024=2^n-1
2^10=2^n-1
n-1=10
n=11 termos