Linear algebra: inverse of the sum of two matrices

In summary, to show that (I-A)^{-1} = I + A + A^2 + A^3 if A^4=0, one can use the formula for inverse sum of matrices and develop a series using I = A(A^-1). By multiplying (I-A) by I+A+A^2+A^3, the solution can be confirmed.
  • #1
degs2k4
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Homework Statement



Show that [tex] (I-A)^{-1} = I + A + A^2 + A^3 [/tex] if [tex]A^4=0[/tex]

The Attempt at a Solution



I found at Google Books some kind of formula for it:
http://books.google.com/books?id=UQ...PA44#v=onepage&q=inverse sum matrices&f=false

However, I think I should develop some kind of series for it using I = A(A^-1), I tried but I haven't been successful...

Thanks in advance.
 
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  • #2
Just multiply (I-A) by I+A+A^2+A^3 and see if you get I.
 
  • #3
Dick said:
Just multiply (I-A) by I+A+A^2+A^3 and see if you get I.

Thanks for your reply, got it solved!
 

1. What is the inverse of the sum of two matrices?

The inverse of the sum of two matrices is the matrix that, when added to the original sum, results in the identity matrix. In other words, it is the matrix that "undoes" the sum and brings it back to its original form.

2. Is the inverse of the sum of two matrices always defined?

No, the inverse of the sum of two matrices is not always defined. It is only defined when the sum of the two matrices is invertible, meaning that their determinants are non-zero.

3. How do you calculate the inverse of the sum of two matrices?

To calculate the inverse of the sum of two matrices, first find the inverse of each individual matrix. Then, add the two inverse matrices together to get the inverse of the sum.

4. Can the inverse of the sum of two matrices be found using the same method as finding the inverse of a single matrix?

No, the method for finding the inverse of the sum of two matrices is different from finding the inverse of a single matrix. While finding the inverse of a single matrix involves finding the determinant and applying a series of operations, finding the inverse of the sum involves finding the individual inverses and adding them together.

5. What is the significance of the inverse of the sum of two matrices in linear algebra?

The inverse of the sum of two matrices plays an important role in solving systems of linear equations. It allows us to "undo" the addition of two matrices and find the original values of the variables in the system. It also has applications in areas such as computer graphics and data analysis.

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