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With reference to the matrix A=[50005000−5]A=\begin{bmatrix}5&0&0\\0&5&0\\0&0&-5\end{bmatrix}, which of the following are TRUE ?

A. |A|=125

B. A is a scalar matrix.

C. A is a diagonal matrix.

D. |A|=-125

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

All off-diagonal entries are zero, so A is diagonal (C true). Its determinant is 5×5×(−5)=−1255\times5\times(-5)=-125 (D true, A false). A scalar matrix needs all diagonal entries equal, but −5≠5-5\ne5, so B is false.

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