Proving Determinants: Int. A & A^-1, Determine detA & detA-1

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SUMMARY

The discussion centers on proving that if matrix A and its inverse A^-1 have integer entries, then both determinants, det A and det A^-1, must equal 1 or -1. The equation det I = det(AA^-1) = det A * det A^-1 establishes that the product of the determinants equals 1. The integer nature of the entries in matrix A restricts the possible values of det A to ±1, confirming that both determinants must be either 1 or -1.

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Homework Statement



If the entries of A and A^-1 are all integers, how do you know that both determinants are 1 or -1?

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The Attempt at a Solution



I know that
1 = det I = detAA-1=detA * detA-1= detA*(1/detA) = 1
Not sure how we get to - or the role integers play in it.

Thanks for your help!
 
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So you have just shown that, if A = A-1, then det A = 1 / det A.
Now consider the values that det A can take if all entries of A are integers.
 
Thanks! I was making the problem harder than it is!
 

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