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## Main Question or Discussion Point

Let A= I - X(X'X)inverseX' to clarify: '=transpose; inverse of quantity (X'X)

1. Must A be a square matrix?

2. Must (X'X) be a square matrix?

3. Must X be a square matrix?

4. Show whether matrix A is an idempotent matrix (i.e. that AA=A)

Thanks.

1. Must A be a square matrix?

2. Must (X'X) be a square matrix?

3. Must X be a square matrix?

4. Show whether matrix A is an idempotent matrix (i.e. that AA=A)

Thanks.