21. Which of the following is a scalar matrix?
Answer: (A) Diagonal matrix with equal diagonal entries
22. If \( A = \begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix} \), what is \( 2A \)?
Answer: (A) \( \begin{bmatrix} 2 & 4 \\ 6 & 8 \end{bmatrix} \)
23. If \( A = \begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix} \), the transpose \( A^T \) is:
Answer: (A) \( \begin{bmatrix} 1 & 3 \\ 2 & 4 \end{bmatrix} \)
24. What is the determinant of \( \begin{bmatrix} 2 & 3 \\ 4 & 5 \end{bmatrix} \)?
Answer: (C) -7
25. If a matrix is singular, its determinant is:
Answer: (B) 0
26. For a system of equations to be consistent, the rank of the coefficient matrix should:
Answer: (B) Equal the rank of the augmented matrix
27. If \( A = \begin{bmatrix} 2 & 4 \\ 6 & 8 \end{bmatrix} \), the adjoint of \( A \) is:
Answer: (A) \( \begin{bmatrix} 8 & -4 \\ -6 & 2 \end{bmatrix} \)
28. The inverse of a matrix exists if:
Answer: (B) The determinant is non-zero
29. If \( A = \begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix} \), the rank of \( A \) is:
Answer: (C) 2
30. The solution of a consistent and independent system of linear equations represents:
Answer: (A) A unique solution
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