Question

Calcule a soma dos 8 primeiros termos da pg (1/27,1/9,1/3...)

Answer 1

P.G.(1/27 ; 1/9 ; 1/3 ; .....)
q = a 2 / a 1
q = 1/9 : 1/27
q = 1/9 x 27/1
q = 27/9
q = 3
a 8 = a 1 . q ^n - 1
a 8 = 1/27 .3^8-1
a 8 = 1/27 . 3^7
a 8 = 1/27 . 2187
a 8 = 2187/27
a 8 = 81
S 8 = a 1 .(q^n    -  1 ) / q - 1
S 8 = 1/27 . (3^8  -  1 ) / 3 - 1
S 8 = 1/27.(3^8  - 1 ) / 2
S 8 = 1/27 (6561  - 1 )  /2
S 8 = 1/27 . 6560 / 2
S 8 = 6560/27 / 2
S 8 = 6560 / 27 X 1/2
S 8 = 6560/54
S 8 = 121,48