alleryWhich of the following is a diagonal matrix?
A$\begin{bmatrix}1&2\\0&3\end{bmatrix}$
B$\begin{bmatrix}0&0\\0&0\end{bmatrix}$
C$\begin{bmatrix}4&0&0\\0&-1&0\\0&0&2\end{bmatrix}$
D$\begin{bmatrix}1&1\\1&1\end{bmatrix}$
Answer & Solution
Correct answer: C. $\begin{bmatrix}4&0&0\\0&-1&0\\0&0&2\end{bmatrix}$
In a diagonal matrix, every non-diagonal entry must be zero.
Option C satisfies this exactly.
Although the zero matrix in option B also has all off-diagonal entries zero, the chapter separately defines zero/null matrix
the clearest standard example of a diagonal matrix here is option C.
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