Invertibility of a product of invertible matrices

In summary, the product of three nxn invertible matrices, ABC, will also be invertible. This is because matrix multiplication is associative, meaning that (AB)C will also be invertible if A and B are invertible. Additionally, if A and B have a non-zero determinant, then their product will also have a non-zero determinant, ensuring invertibility. This can be extended to any number of factors through the use of associativity and the concept of bijective linear maps.
  • #1
tobias_funke
1
0
If A,B, and C are each nxn invertible matrices, will the product ABC be invertible?
 
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  • #2
yea, if A, B are nxn invertible then AB is invertible. Since Matrix Multiplication is associative, (AB)C is invertible provided c is nxn invertible.
 
  • #3
If your linear algebra is better than your basic set/function theory, remark that A,B,C have non-zero determinant, hence their product also.
 
  • #4
If A and B are both invertible then [itex](AB)(B^{-1}A^{-1})= A(B^{-1}B)A^{-1}[/itex] because, as jakncoke says, matrix multiplication is associative. Of course, [itex]B^{-1}B= I[/itex] so that becomes [itex](AB)(B^{-1}A^{-1})= AA^{-1}= I[/itex]. Simlarly, [itex](B^{-1}A^{-1})(AB)= B^{-1}(A^{-1}A)B^{-1}= B^{1}B= I[/itex]

You can extend that to any number of factors by induction and repeated use of associativity.
 
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  • #5
As Landau referenced, if you like to think about functions, matrix multiplication is equivalent to applying a linear map, and invertible matrices define bijective linear maps (and vice versa), and a composition of bijective linear maps is a bijective linear map. so yes.
 

Related to Invertibility of a product of invertible matrices

1. What does it mean for a matrix to be invertible?

A matrix is invertible if it has an inverse, which is another matrix that when multiplied with the original matrix results in the identity matrix (a square matrix with 1's on the main diagonal and 0's everywhere else). This means that the original matrix can be "undone" or reversed, similar to how multiplying by a number's reciprocal "undoes" multiplication.

2. How do you determine if a matrix is invertible?

One way to determine if a matrix is invertible is by calculating its determinant. If the determinant is non-zero, the matrix is invertible. Another way is to check if the matrix has linearly independent columns or rows. If both conditions are met, then the matrix is invertible.

3. What is the significance of invertible matrices?

Invertible matrices have many applications in mathematics, engineering, and science. They are used in solving systems of linear equations, calculating areas and volumes, and in computer graphics and cryptography. Invertible matrices also have a special property that allows for efficient computation of their inverse.

4. Can a product of invertible matrices be invertible?

Yes, a product of invertible matrices can still be invertible. In fact, the inverse of a product of matrices is equal to the product of their individual inverses in reverse order. This property is known as the inverse of a product property.

5. What happens if one of the matrices in a product of invertible matrices is not invertible?

If one of the matrices in a product of invertible matrices is not invertible (also known as singular), then the entire product is also not invertible. This is because the inverse of a singular matrix does not exist. However, the remaining matrices in the product may still be invertible, and their inverse can be calculated separately.

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