JEE Mains · Maths · STD 12 - 3 and 4 . metrices and determinant
Let \(A=\left\{a_{i}\right\}\) be a \(3 \times 3\) matrix, where \(a_{i j}=\left\{\begin{aligned}(-1)^{j-i} & \text { if } i < j \\ 2 & \text { if } i=j \\(-1)^{i+j} & \text { if } i > j \end{aligned}\right.\) then \(\operatorname{det}\left(3 \operatorname{Adj}\left(2 \mathrm{~A}^{-1}\right)\right)\) is equal to \(.....\)
- A \(126\)
- B \(12\)
- C \(144\)
- D \(108\)
Answer & Solution
Correct Answer
(D) \(108\)
Step-by-step Solution
Detailed explanation
\(A=\left[\begin{array}{ccc}2 & -1 & 1 \\ -1 & 2 & -1 \\ 1 & -1 & 2\end{array}\right]\) \(|\mathrm{A}|=4\) \(\left|3 \operatorname{adj}\left(2 \mathrm{~A}^{-1}\right)\right|=\left|3 \cdot 2^{2} \operatorname{adj}\left(\mathrm{A}^{-1}\right)\right|\)…
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