Proving Idempotency and Nonsingularity of Matrix A

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In summary, the conversation discusses the concept of idempotent matrices and how to show that I-A is also idempotent. It also mentions the difficulty in solving part B and a potential solution involving adding I to both sides.
  • #1
Roni1985
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Homework Statement



Let A be an idempotent matrix (A^2=A)
a) show that I-A is also idempotent
b) show that I+A is nonsingular and (I+A)^(-1)=I-(1/2)*A


Homework Equations





The Attempt at a Solution



I managed to solve part a, but have a little problem solving b.

I tried
(I+A)*(I+A)^(-1)=(?)I

but didn't know how to treat (I+A)^(-1)

Thanks,
Roni.
 
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  • #2
You are given that A2 = A.
Adding I to both sides gives us
A2 + I = A + I
==> |A2 + I| = |A + I|

Can you do anything with that?
 
  • #3
Mark44 said:
You are given that A2 = A.
Adding I to both sides gives us
A2 + I = A + I
==> |A2 + I| = |A + I|

Can you do anything with that?

oh, nice approach.
Thanks for the help.
I'll try the second part of B
 

FAQ: Proving Idempotency and Nonsingularity of Matrix A

What is idempotency in a matrix?

Idempotency in a matrix refers to the property of a matrix where multiplying the matrix by itself results in the same matrix. In other words, the matrix remains unchanged after being multiplied by itself.

How can we prove idempotency of a matrix?

To prove idempotency of a matrix, we need to calculate the product of the matrix with itself. If the resulting matrix is equal to the original matrix, then it is idempotent.

What does nonsingularity of a matrix mean?

Nonsingularity in a matrix refers to the property where the matrix has a unique inverse. In other words, the determinant of the matrix is non-zero.

How can we prove nonsingularity of a matrix?

To prove nonsingularity of a matrix, we need to calculate the determinant of the matrix. If the determinant is non-zero, then the matrix is nonsingular.

Why is it important to prove idempotency and nonsingularity of a matrix?

Proving idempotency and nonsingularity of a matrix is important in various mathematical and scientific applications. For example, in linear algebra, idempotency and nonsingularity of a matrix are used to solve systems of equations and to find eigenvalues and eigenvectors. In engineering and computer science, these properties are used in optimization and data analysis techniques. Therefore, proving these properties is crucial in understanding and utilizing matrices in various fields.

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