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If (x)^(1/3) + (1/x)^(1/3)= 3 then x^3 + (1/x)^3 = ?

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If (x)^(1/3) + (1/x)^(1/3)= 3 then x^3 + (1/x)^3 = ?
posted Jun 17, 2019 by anonymous

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1 Answer

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(x)^(1/3) + (1/x)^(1/3)= 3 ----- A
[ cubing both sides using (a + b)^3 = a^3 + b^3 + 3(a^2)(b) + 3(a)(b^2) ]

x + (1/x) + 3*[(x)^(1/3) + (1/x)^(1/3)] = 27
From A [(x)^(1/3) + (1/x)^(1/3)] = 3

x + (1/x) + 3*3 = 27
x = [9 + (4*(5^(1/2)))] & [9 - (4*(5^(1/2)))]
therefore

x^3 + (1/x)^3 = 5778.

answer Aug 5, 2019 by Tejas Naik
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