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## Homework Statement

Prove that [P]^2=[P] (that the matrix is idempotent)

## Homework Equations

## The Attempt at a Solution

A(A^T*A)^-1 A^T= (A(A^T*A)^-1 A^T)^2

Where A^T is the transpose of A. I have no idea.

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- Thread starter TheBuddha11
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Prove that [P]^2=[P] (that the matrix is idempotent)

A(A^T*A)^-1 A^T= (A(A^T*A)^-1 A^T)^2

Where A^T is the transpose of A. I have no idea.

- #2

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Backing up a bit further, what is the definition of an orthogonal projection matrix?

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