Solve Idempotent Matrix Inequality: n≥p-1 | Artin's Algebra

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SUMMARY

The discussion focuses on proving that for a prime number p, an nxn integer matrix A, which satisfies the condition A^p = I (where I is the identity matrix), must have a dimension n that is greater than or equal to p-1. The participants highlight that since A is not the identity matrix, it is invertible, as demonstrated by the equation A^(p-1) = A^-1. Additionally, they note the polynomial equation A^(p+1) - A = A(A^p - I) = 0, which is crucial for the proof.

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Homework Statement



This is from Chapter 11 of Artin's Algebra:

Let p be a prime, and let A (not the identity) be an nxn integer matrix such that A^{p}=I. Prove that n \geq p-1.

Homework Equations



This is in the factorization chapter, and the section is called Explicit Factorization of Polynomials.

The Attempt at a Solution



I don't even know where to begin. I'm guessing I need to somehow get a polynomial equation, but like I said, I don't really know where to start. Any help would be greatly appreciated!
 
Last edited:
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haven't got there yet, but hopefully these help you get started

clearly A is invertible as A^(p-1) = A^-1

also note that
A^(p+1) - A = A(A^p - I ) = 0
 

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