Según mi punto de vista ... el ejercicio se desarrolla de la siguiente manera
Hola
Primero
(a + b)^2 = a^2 + b^2 + 2 a b
1) a b = (1/2) (a + b)^2 - (1/2) (a^2 + b^2))
Por otro lado
(a + b)^3 = a^3 + b^3 + 3 a^2 b + 3 a b^2
(a + b)^3 = (a^3 + b^3) + 3 a b (a + b)
deducimos
a^3 + b^3 = (a + b)^3 - 3 a b (a + b)
De 1)
a^3 + b^3 = (a + b)^3 - 3 ((1/2) (a + b)^2 - (1/2) (a^2 + b^2))) (a + b)
a^3 + b^3 = (a + b)^3 - (3/2) (a + b)^3 + (3/2) (a + b) (a^2 + b^2)
a^3 + b^3 = (3/2) (a + b) (a^2 + b^2) - (1/2) (a + b)^3
==============
Con los valores dados
a^3 + b^3 = (3/2) (1) (2) - (1/2) (1)^3
a^3 + b^3 = 3 - (1/2)
a^3 + b^3 = 5/2
*************************
Verificamos
a b = ( (a + b)^2 - (a^2+b^2) )/2 = ( 1^2 - 2)/2 = -1/2
Como
a + b = 1
a y b son soluciones de
x^2 - x - (1/2) = 0
x^2 - x = (1/2)
x^2 - 2 (1/2) x + (1/4) = (1/2) + (1/4)
(x - (1/2))^2 = 3/4
a;b = (1 +/- √3)/2
a^2 = (1 - 2 √3 + 3)/4
b^2 = (1 + 2 √3 + 3)/4
a^2 + b^2 = 2
a^3 = (1 - 3 (√3) + 3 (√3)^2 - (√3)^2)/8
b^3 = (1 + 3 (√3) + 3 (√3)^2 + (√3)^2)/8
a^3 + b^3 = 2*(1 + 9) /8
******
Saludos
a vale 1.87
b vale -0.13
por tanto a3+b3= 6.563-0.002=6.559
enjoy mate5
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Answers & Comments
Según mi punto de vista ... el ejercicio se desarrolla de la siguiente manera
Hola
Primero
(a + b)^2 = a^2 + b^2 + 2 a b
1) a b = (1/2) (a + b)^2 - (1/2) (a^2 + b^2))
Por otro lado
(a + b)^3 = a^3 + b^3 + 3 a^2 b + 3 a b^2
(a + b)^3 = (a^3 + b^3) + 3 a b (a + b)
deducimos
a^3 + b^3 = (a + b)^3 - 3 a b (a + b)
De 1)
a^3 + b^3 = (a + b)^3 - 3 ((1/2) (a + b)^2 - (1/2) (a^2 + b^2))) (a + b)
a^3 + b^3 = (a + b)^3 - (3/2) (a + b)^3 + (3/2) (a + b) (a^2 + b^2)
a^3 + b^3 = (3/2) (a + b) (a^2 + b^2) - (1/2) (a + b)^3
==============
Con los valores dados
a^3 + b^3 = (3/2) (1) (2) - (1/2) (1)^3
a^3 + b^3 = 3 - (1/2)
a^3 + b^3 = 5/2
*************************
Verificamos
a b = ( (a + b)^2 - (a^2+b^2) )/2 = ( 1^2 - 2)/2 = -1/2
Como
a + b = 1
a y b son soluciones de
x^2 - x - (1/2) = 0
x^2 - x = (1/2)
x^2 - 2 (1/2) x + (1/4) = (1/2) + (1/4)
(x - (1/2))^2 = 3/4
a;b = (1 +/- √3)/2
a^2 = (1 - 2 √3 + 3)/4
b^2 = (1 + 2 √3 + 3)/4
a^2 + b^2 = 2
a^3 = (1 - 3 (√3) + 3 (√3)^2 - (√3)^2)/8
b^3 = (1 + 3 (√3) + 3 (√3)^2 + (√3)^2)/8
a^3 + b^3 = 2*(1 + 9) /8
a^3 + b^3 = 5/2
******
Saludos
a vale 1.87
b vale -0.13
por tanto a3+b3= 6.563-0.002=6.559
enjoy mate5