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Enunciado

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solución

 

       

x + 1/x = √ 2   ,

          1
qué vale  x 777  +  ――
          x 777


   Este problema se puede resolver empleando las propiedades de las funciones simétricas.

Una función es simétrica, si intercambiando cualesquiera de sus variables el valor de la función no varía

x = α ,  1/x = β

α + β = √ 2   
α β = 1 

 

 

 

 

 

 

 

 

 

 

 

   


Como es bien conocido, relaciones de Cardano-Vieta , α y β son raíces de la ecuación,

ξ 2 − √ 2   ∙ ξ + 1 = 0

α = √ 2   /2 ∙ ( 1 + i ) = е i ∙ π/4
 β = √ 2   /2 ∙ ( 1 − i ) = е i ∙ π/4


Sólo resta evaluar α y β elevadas a la 777 potencia,

777 = 4 ∙ 194 + 1

е π ∙ 777/4 = е π ∙ 194 ∙ е π/4 = е π ∙ 2 ∙ е π/4 = е π/4

∴   x 777 = x


De dónde,

1 
x 777  +  ―― =  √ 2   
x 777


EnglishEspañol

 

 

 

 

 

   

Statement

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer

       

x + 1/x = √ 2   ,

          1
calculate  x 777  +  ――
          x 777


   This is a problem on symmetric functions.

A function is symmetric if the exchange of its variables does not alters its value

x = α ,  1/x = β

α + β = √ 2   
α β = 1 

 

 

 

 

 

 

 

 

 

 

 

   


As it is well known, Vieta's formula , α and β are roots of the equation,

ξ 2 − √ 2   ∙ ξ + 1 = 0

α = √ 2   /2 ∙ ( 1 + i ) = е i ∙ π/4
 β = √ 2   /2 ∙ ( 1 − i ) = е i ∙ π/4


Evaluating α and β to the 777 power,

777 = 4 ∙ 194 + 1

е π ∙ 777/4 = е π ∙ 194 ∙ е π/4 = е π ∙ 2 ∙ е π/4 = е π/4

∴   x 777 = x


Whence,

1 
x 777  +  ―― =  √ 2   
x 777



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