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 :
- A 56
- B 132
- C 174
- D 280
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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