Proving Similarity of Matrices: A^2=C to B^2=C

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In summary, the conversation revolves around proving the statement that if A^2=C and A~B, then B^2=C. However, the validity of this statement depends on the value of the matrix C, as it would be different if C was 0 or any other multiple of the identity matrix. The speaker also mentions that the book has A^2=O, but it is unclear if it is referring to zero or the letter O.
  • #1
eyehategod
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I need help with this proof. Can anyone lead me in the right direction?

Let A be an nxn matrix such that A^2=C.
Prove that if B~A, then B^2=C.
 
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  • #2
Let A=diag(1,2), B=diag(2,1). A^2=diag(1,4), B^2=diag(4,1). A~B. A^2 is not equal to B^2. Is there something you aren't telling us about C or do you want to prove A^2~B^2?
 
  • #3
I gave you exactly what the book says
 
  • #4
eyehategod said:
I gave you exactly what the book says

If that's exactly what the book says, then you can't prove it. Because it's false.
 
  • #5
what if C were to be 0. Would that proof make sense?
 
  • #6
eyehategod said:
what if C were to be 0. Would that proof make sense?

It makes all of the difference in the world. If A^2=0 and A~B then B^2=(PAP^(-1))(PAP^(-1)). What's that?
 
  • #7
that would be:
B^2=P^(-1)A^(2)P
B^2=P^(1)0P=0
 
  • #8
It would also be very different if C were any other multiple of the identity matrix. Wouldn't it?
 
  • #9
THe book really has instead of A^2=C its A^2=O.But I can't tell if its zero or the letter O. THe O is at a slant if that means anything
 
  • #10
eyehategod said:
that would be:
B^2=P^(-1)A^(2)P
B^2=P^(1)0P=0

Yes.
 
  • #11
eyehategod said:
THe book really has instead of A^2=C its A^2=O.But I can't tell if its zero of the letter O. THe O is at a slant if that means anything

I don't know. But as I said any multiple of the identity would work as well as 0.
 

Q: What is the definition of similarity of matrices?

Similarity of matrices refers to the property of two matrices having the same size and the same pattern of entries. This means that the two matrices have the same number of rows and columns, and the corresponding entries in each matrix have the same value.

Q: How is similarity of matrices proven?

To prove similarity of matrices, we need to show that there exists a non-singular matrix that transforms one matrix into the other. This means that the two matrices can be transformed into each other through a series of elementary row or column operations.

Q: What is the significance of proving similarity of matrices?

Proving similarity of matrices is important because it allows us to simplify and solve complex systems of linear equations. It also helps us to understand the structure and properties of matrices, which are essential in many areas of mathematics and science.

Q: What are the conditions for proving similarity of matrices?

The two matrices must have the same size and rank in order to be considered similar. Additionally, they must have the same eigenvalues and eigenvectors, which can be determined through diagonalization or Jordan canonical form. Finally, the two matrices must be transformable into each other through a non-singular matrix.

Q: What is the difference between proving similarity and congruence of matrices?

Similarity of matrices involves the transformation of one matrix into another using a non-singular matrix, while congruence of matrices involves the transformation of one matrix into another using an orthogonal matrix. In simpler terms, similarity focuses on the pattern of entries in the matrices, while congruence focuses on the orientation and size of the matrices.

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