How do I see this? Simplification

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SUMMARY

The discussion centers on the difficulty of proving the equation involving the product of roots of unity, specifically the relationship between the polynomial \(X^n - 1\) and its factorization through cyclotomic polynomials \(\Phi_d\). The user attempts to establish that \(X^n - 1 = \prod_{1 \leq d \leq n \quad d | n} \Phi_d\), where \(\Phi_d = \prod_{0 \leq i \leq d-1 \quad \text{gcd}(d,i)=1} (X - \omega_d^i)\) and \(\omega_d = \exp{(2 \pi i / d)}\). The user acknowledges an error in their understanding and expresses uncertainty about proving the equivalence of the two product forms. The example with \(n = 6\) illustrates the discrepancy between the left-hand side and right-hand side of the original equation.

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  • Familiarity with the concept of roots of unity
  • Knowledge of the greatest common divisor (gcd) in number theory
  • Basic proficiency in polynomial algebra and factorization
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Mathematicians, students of algebra, and anyone interested in polynomial factorization and number theory concepts, particularly those dealing with cyclotomic fields and roots of unity.

nonequilibrium
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How do I see that for any natural non-zero n:

[itex]\left( \prod_{1 \leq d \leq n \quad d | n} \right) \left( \prod_{0 \leq i \leq d-1 \quad \textrm{gcd}(d,i)=1} \right) a_i = \prod_{0 \leq i \leq n-1} a_i[/itex]?
 
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I would say this is going to be hard to prove. EXCEEDINGLY hard to prove. Because... it's not true. For instance, letting n = 6, the LHS is

[tex] a_0 a_1^3 a_2 a_5[/tex]

The RHS, of course, is

[tex] a_0 a_1 a_2 a_3 a_4 a_5[/tex]

Or maybe I don't understand your notation?
 
Well that explains why I couldn't prove it :p

I was (am) trying to prove that [itex]X^n - 1 = \left( \prod_{1 \leq d \leq n \quad d | n} \right) \Phi_d[/itex] where [itex]\Phi_d = \left( \prod_{0 \leq i \leq d-1 \quad \textrm{gcd}(d,i)=1} \right) (X - \omega_d^i)[/itex] where [itex]\omega_d = \exp{ (2 \pi i /d) }[/itex]

The RHS of my original equation can be understood by noting that [itex]X^n-1=\prod_{0 \leq i \leq n} (X-\omega_n^i)[/itex]

but I now see my error... My apologies

However, I'm still not sure how to prove the above equation, aka that

[itex]\prod_{0 \leq i \leq n} (X-\omega_n^i) = \left( \prod_{1 \leq d \leq n \quad d | n} \right) \left( \prod_{0 \leq i \leq d-1 \quad \textrm{gcd}(d,i)=1} \right) (X - \omega_d^i)[/itex]
 

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