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JEE Main 2020
Matrices & Determinants
Matrices and Determinants
Hard

Question

If A=15!6!7![5!6!7!6!7!8!7!8!9!]\mathrm{A}=\frac{1}{5 ! 6 ! 7 !}\left[\begin{array}{ccc}5 ! & 6 ! & 7 ! \\ 6 ! & 7 ! & 8 ! \\ 7 ! & 8 ! & 9 !\end{array}\right], then adj(adj(2 A))|\operatorname{adj}(\operatorname{adj}(2 \mathrm{~A}))| is equal to :

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Solution

This problem tests your understanding of properties of determinants, especially those related to scalar multiplication of matrices and adjugate matrices. We will systematically break down the problem using these properties.

1. Key Concepts and Formulas

For an n×nn \times n matrix MM:

  • Determinant of a scalar multiple: kM=knM|kM| = k^n |M|, where kk is a scalar.
  • Determinant of the adjugate: adj(M)=Mn1|\operatorname{adj}(M)| = |M|^{n-1}.
  • Determinant of the adjugate of adjugate: adj(adj(M))=M(n1)2|\operatorname{adj}(\operatorname{adj}(M))| = |M|^{(n-1)^2}.

In this problem, the matrix AA

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