Serie derazones geométricas iguales y continuas = > a / b = b / c = c / d = k .
(I)
"hallar el ultimo antecedente" = > a + b + c + d = ?
"la suma de las cuatro razones es 4 / 3" = > a / b + b / c + c / d + d / e = 4 / 3 = > k + k + k + k = 4 / 3 = > 4k = 4 / 3 = > k = 1 / 3
Reemplazamos en (I) = > a / b = 1 / 3 = > a = 1 / 3b = > b / c = 1 / 3 = > b = 1 / 3c = > c / d = 1 / 3 = > c = 1 / 3d = > d / e = 1 / 3 = > e = 1 / 3e
Reemplazamos hacia atrás : = > a = 1 / 3(1 / 3c) = > a = 1 / 3(1 / 3(1 / 3d)) = > a = 1 / 27
hallamos d : = > d = 1 / 3e = > d = 1 / 3(640) = > d = 81
Hallamos c : = > c = 1 / 3d = > c = 1 / 3(1024) = > c = 72
Hallamos b : = > b = 5 / 8c = > b = 5 / 8(640) = > b = 36
Hallamos a : = > a = 1 / 27d = > a = 1 / 27(1024) = > a = 90
La suma de los antecedentes : = > a + b + c + d = 90 + 36 + 72 + 81 = > a + b + c + d = 279.