Question

Quantos termos tem a pg (4,20,100,...,12.500)?

Answer 1

Razão: 20/4 = 5

A1 = 4
An = 12500

An = a1 . q^n-1
12500 = 4 , 5^n-1
12500 / 4 = 5^n-1
3125 = 5^n-1

fatorando o 3125

3125 /5
625 / 5
125 / 5
25 /5
5 /5
1 

5^5 = 5^n-1

cortando as bases

5 = n-1
5+1 = n
6 = n