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JEE Mains · Maths · STD 12 - 3 and 4 . metrices and determinant

For a \(3 \times 3\) matrix \(M\), let trace \((M)\) denote the sum of all the diagonal elements of \(M\). Let \(A\) be a \(3 \times 3\) matrix such that \(|A|=\frac{1}{2}\) and trace \((A)=3\). If \(B=\operatorname{adj}(\operatorname{adj}(2 A))\), then the value of \(|B|+\) trace (B) equals :

  1. A 56
  2. B 132
  3. C 174
  4. D 280
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Answer & Solution

Correct Answer

(D) 280

Step-by-step Solution

Detailed explanation

\(\because \operatorname{tr}(A)=3 \text { and }|A|=\frac{1}{2}\) Now, \(B=\operatorname{adj}(\operatorname{adj}(2 A))=|2 A|^{3-2} \cdot(2 A)\) \(=2^3|A| \cdot 2 A=8 A\)…
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