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

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    Determinants
In summary, a determinant is a mathematical value used to determine properties of a square matrix, such as invertibility. It can be calculated using various methods depending on the matrix. Proving determinants is important for practical applications. To prove A times A^-1 equals the identity matrix, properties of determinants are used. The determinants of A and A^-1 can be determined separately using the properties and formula for the determinant of the inverse of a matrix.
  • #1
tatianaiistb
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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?

Homework Equations





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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  • #2
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.
 
  • #3
Thanks! I was making the problem harder than it is!
 

1. What is a determinant?

A determinant is a mathematical value that is calculated from the entries of a square matrix. It is used to determine certain properties of the matrix, such as whether it is invertible or singular.

2. How do you calculate the determinant of a matrix?

The determinant of a matrix can be calculated using various methods, such as the cofactor expansion method or the row reduction method. The specific method used will depend on the size and complexity of the matrix.

3. What is the significance of proving determinants?

Proving determinants is important because it allows us to determine whether a matrix is invertible or singular, which has many practical applications in fields such as engineering, physics, and economics.

4. How do you prove that A times A^-1 equals the identity matrix?

To prove that A times A^-1 equals the identity matrix, we can use the definition of the inverse of a matrix and the properties of determinants to show that the product of the two matrices results in the identity matrix.

5. Can you determine the determinants of A and A^-1 separately?

Yes, the determinants of A and A^-1 can be determined separately by using the properties of determinants and the formula for the determinant of the inverse of a matrix.

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