alleryA square matrix $A$ is orthogonal when
A$A+A'=I$
B$A'=A$
C$AA'=I$ and $A'A=I$
DAll diagonal elements are equal to 1
Answer & Solution
Correct answer: C. $AA'=I$ and $A'A=I$
An orthogonal matrix satisfies $AA'=I$ and also $A'A=I$.
This means its transpose acts as its inverse.
Merely having 1s on the diagonal does not guarantee orthogonality.
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