A square matrix $A$ satisfies $A^T A = I$. Such a matrix is called:

Question

Accepted Answer

C. Orthogonal

An orthogonal matrix satisfies $A^T A = A A^T = I$, equivalently $A^{-1} = A^T$.
Its rows (and columns) form an orthonormal set.
Rotation and reflection matrices in $\mathbb{R}^n$ are orthogonal.
$|A|$ for an orthogonal matrix is always $\pm 1$.

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Symmetric

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Skew-symmetric

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Nilpotent

A square matrix $A$ satisfies $A^T A = I$. Such a matrix is called:

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