Finding Polynomials from their Zeros

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SUMMARY

The discussion focuses on proving the irrationality of the expression x = 2^(1/2) + 2^(1/3). Participants emphasize the need to demonstrate that x satisfies a polynomial equation of the form x^6 + a_1*x^5 + ... + a_0 = 0 with integer coefficients. Initial attempts to manipulate the expression through multiplication of factors were unsuccessful, prompting suggestions to start from x = sqrt(2) + cbrt(2) and derive a suitable polynomial equation. The goal is to find a polynomial that x satisfies to establish its irrationality definitively.

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Homework Statement


Prove that x = 2^(1/2)+2^(1/3) is irrational.


Homework Equations





The Attempt at a Solution



The hint to the exercise says that I should first show that x satisfies an equation of the form x^6+a_1*X^5+...+a_0 = 0, where the coefficients are integers.

I am having trouble showing that x satisfies such an equation.

I tried multiplying (x-2^(1/2)-2^(1/3))(x+2^(1/2)-2^(1/3)) but was not successful in getting integer coefficients.
 
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Try putting some more factors in. Or just start from

x=sqrt(2)+cbrt(2)

and manipulate it to find an expression x satsifies. (eg, if x=sqrt(2), then squaring both sides yields x^2=2, so x satisfies x^2-2=0. n.b. don't square both sides of what you started wit -try something more sophisticated than that).
 

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