Proving Symmetry of AAT: Is it Possible?

In summary, to show that AAT is symmetric for any matrix A, we can use the equation AAT = (AT)TAT and the fact that (AT)T = A and AT = AT to prove that AAT is symmetric.
  • #1
KillerZ
116
0

Homework Statement



A matrix S is symmetric if S = ST. Show that AAT is symmetric for any matrix A.

Homework Equations



AAT = (AT)TAT

The Attempt at a Solution



I just said:

A = (AT)T and AT = AT

Therefore AAT is symmetric.

I am unsure if that proves it or if I just went in a circle proving nothing.
 
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  • #2
If [tex] A, B [/tex] are any matrices, how do you simplify the following expression?

[tex]
\left(AB\right)^T
[/tex]

Apply that answer to simplify

[tex]
A A^T
[/tex]

and use the hints you provided
 
  • #3
Ok I think this is right.

(AB)T = BTAT

Then (AAT)T = AAT

Therefore AAT is symmetric because (AT)T = A and AT = AT.
 
  • #4
I think you have the correct idea. the 'conventional' way of finishing the proof would be to write everything in one string rather than stopping midstream - I have no idea how
picky your professor would be in that regard.
 

FAQ: Proving Symmetry of AAT: Is it Possible?

1. How do you determine if a matrix is symmetric?

To determine if a matrix is symmetric, you must first check if it is a square matrix (same number of rows and columns). Then, you can compare the elements in the matrix to their corresponding elements in the transpose of the matrix. If they are equal, the matrix is symmetric.

2. What is the definition of a symmetric matrix?

A symmetric matrix is a square matrix where the elements are equal to their corresponding elements in the transpose of the matrix. In other words, the matrix is unchanged when it is flipped over its diagonal.

3. Can a non-square matrix be symmetric?

No, a non-square matrix cannot be symmetric. The definition of a symmetric matrix requires that the matrix is square, meaning it has the same number of rows and columns.

4. How can you show a matrix is symmetric using mathematical notation?

To show a matrix is symmetric using mathematical notation, you can write out the matrix and its transpose and compare the corresponding elements. If they are equal, you can write out the equation A = AT, where A is the original matrix and AT is its transpose.

5. What is the significance of a symmetric matrix in mathematics?

Symmetric matrices have many applications in mathematics, including in linear algebra, geometry, and optimization. They are also used in physics and engineering to represent real-world systems and their properties. Additionally, symmetric matrices have special properties that make them easier to work with and solve compared to non-symmetric matrices.

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