# When $$A^T = A^{-1}$$?

Algebra Level pending

If $$A$$ is a square matrix and $$A^T A= I ,$$ the Identity matrix.

Which of the following is true?

$$a. \$$Each column of $$A$$ has unit length and is perpendicular to every other column.

$$b. \ A$$ is an orthogonal matrix.

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