Question

calcule a soma dos 20 termos iniciais da série 1 + 1/3 + 1/27 + 1/81 +...

Answer 1

Sn =a1(qⁿ-1)/(q-1)
S20 = 1[(1/3)²⁰-1)/(1/3-1)]
S20= (1/3²⁰ - 1)/(-2/3) 
S20 = (1- 1/3²⁰)/(2/3)
S20 = (3²⁰- 1)/3²⁰ . 3/2
S20 = (3²⁰ -1)/(2.3¹⁹)