Question

Calcular a soma dos seis primeiros termos da PG (5,15,45...)

Answer 1

(5,15,45,135,405,1215)

Answer 2

S n = a 1 . q^n  -  1  / q - 1 
q = a 2 / a 1
q = 15/5
q = 3
S 6 = 5. (3^6     -   1 ) / q - 1
 S 6 = 5. (729  -  1 ) / 3 - 1
S 6 = 5 . (728) / 2
S 6 = 3641 / 2
S 6 = 1820.