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

Let \(I\) be the identity matrix of order \(3 \times 3\) and for the matrix \(\mathrm{A}=\left[\begin{array}{ccc}\lambda & 2 & 3 \\ 4 & 5 & 6 \\ 7 & -1 & 2\end{array}\right],|\mathrm{A}|=-1\). Let B be the inverse of the matrix \(\operatorname{adj}\left(\mathrm{A} \operatorname{adj}\left(\mathrm{A}^2\right)\right)\). Then \(|(\lambda B+1)|\) is equal to _____

  1. A 30
  2. B 32
  3. C 36
  4. D 38
Verified Solution

Answer & Solution

Correct Answer

(D) 38

Step-by-step Solution

Detailed explanation

\begin{aligned} & |A|=\left|\begin{array}{ccc} \lambda & 2 & 3 \\ 4 & 5 & 6 \\ 7 & -1 & 2 \end{array}\right|=-1 \\ & \lambda(16)-2(-34)+3(-39)=-1 \\ & 16 \lambda=48 \Rightarrow \lambda=3 \\ & \mathrm{~B}^{-1}=\operatorname{adj}\left(\mathrm{A} \cdot…

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