Medium MCQ +4 / -1 PYQ · JEE Mains 2023

Let $x,y,z > 1$ and $$A = \left[ {\matrix{ 1 & {{{\log }_x}y} & {{{\log }_x}z} \cr {{{\log }_y}x} & 2 & {{{\log }_y}z} \cr {{{\log }_z}x} & {{{\log }_z}y} & 3 \cr } } \right]$$. Then $\mathrm{|adj~(adj~A^2)|}$ is equal to

  1. A $6^4$
  2. B $2^8$ Correct answer
  3. C $4^8$
  4. D $2^4$

Solution

$$ \begin{aligned} & |A|=\frac{1}{\log x \log y \log z}\left|\begin{array}{ccc} \log x & \log y & \log z \\ \log x & 2 \log y & \log z \\ \log x & \log y & 3 \log z \end{array}\right|=\left|\begin{array}{ccc} 1 & 1 & 1 \\ 1 & 2 & 1 \\ 1 & 1 & 3 \end{array}\right|=2 \\\\ & \Rightarrow\left|\operatorname{adj}\left(\operatorname{adj} A^2\right)\right|=\left|\operatorname{adj}\left(A^2\right)\right|^2=\left(\left|A^2\right|^2\right)^2=|A|^8=2^8 \end{aligned} $$

About this question

Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations

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