Question

calcule a soma dos termo da pg(1;1/3;...;1/81)

Answer 1

a1 = 1
a2 = 1/3
a1q = 1/3
1q = 1/3
q = 1/3 : 1/1 = 1/3 * 1/1  = 1/3 ***
an = 1/81

an = a1. qⁿ⁻¹
an = 1.( 1/3)ⁿ⁻¹
Nota :  1/81 = ( 1/3)⁴
( 1/3)⁴ = ( 1/3)ⁿ⁻¹
n - 1 = 4
n = 4 + 1
n =5 ***
S5  = 1 [ ( 1/3)⁵  - 1 ]/( 1/3 - 1/1)
S5 =  ( 1/243) / ( -2/3)
S5 = 1/243 : ( - 2/3)  = 1/243 * ( -3/2) = - 3/486  = - ( 1/162) ***