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COMEDK · Maths · 22. Determinants

Given \(P = \begin{bmatrix} 2 & \alpha & 1 \\ 1 & 2 & 2 \\ 1 & 3 & 3 \end{bmatrix}\) is the adjoint of a \(3 \times 3\) matrix A and \(|A| = 3\), then the value of \(\alpha\) is:

  1. A \(-8\)
  2. B \(-26\)
  3. C \(7\)
  4. D \(-25\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(-8\)

Step-by-step Solution

Detailed explanation

Given \(P = \text{adj}(A)\) and \(A\) is a \(3 \times 3\) matrix. We know that \(|\text{adj}(A)| = |A|^{n-1}\), where \(n\) is the order of the matrix. Here, \(n = 3\) and \(|A| = 3\). \(|P| = |A|^{3-1} = |A|^2 = 3^2 = 9\) Now, calculating the determinant of matrix \(P\):…