🛠️ JEE➗ Maths

Let \(P=\left[{p}_{ij}\right]\)and \(Q=\left[{q}_{ij}\right]\) be two square matrices of order \(3\) such that \({q}_{ij…

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Let \(P=\left[{p}_{ij}\right]\)and \(Q=\left[{q}_{ij}\right]\) be two square matrices of order \(3\) such that \({q}_{ij}={2}^{\left(i+j−1\right)}{p}_{ij}\) and \(det\left(Q\right)={2}^{10}\). Then the value of \(det\left(adj\left(adjP\right)\right)\) is:

[JEE Main 2026, 24 Jan (Shift 2)]

a

81

b

32

c

124

d

16

✓ Correct answer: d)

16

Explanation

\(\left|Q\right|=\left|\begin{matrix}2{\text{p}}_{11} & {2}^{2}{\text{p}}_{12} & {2}^{3}{\text{p}}_{13} \\ {2}^{2}{\text{p}}_{21} & {2}^{3}{\text{p}}_{22} & {2}^{4}{\text{p}}_{23} \\ {2}^{3}{\text{p}}_{31} & {2}^{4}{\text{p}}_{32} & {2}^{5}{\text{p}}_{33}\end{matrix}\right|={2}^{10}\)

\(\Rightarrow {2}^{2}⋅2⋅{2}^{3}\left|\begin{matrix}{\text{p}}_{11} & {\text{p}}_{12} & {\text{p}}_{13} \\ 2{\text{p}}_{21} & 2{\text{p}}_{22} & 2{\text{p}}_{23} \\ {2}^{2}{\text{p}}_{31} & {2}^{2}{\text{p}}_{32} & {2}^{2}{\text{p}}_{33}\end{matrix}\right|={2}^{10}\)

\(\Rightarrow {2}^{9}\left|\begin{matrix}{\text{p}}_{11} & {\text{p}}_{12} & {\text{p}}_{13} \\ {\text{p}}_{21} & {\text{p}}_{22} & {\text{p}}_{23} \\ {\text{p}}_{31} & {\text{p}}_{32} & {\text{p}}_{33}\end{matrix}\right|={2}^{10}\)

\(\Rightarrow |\text{P}|=2\)

\(|\operatorname{adj}(\operatorname{adj}(P))|=|P|^{(n-1)^2}\)

\(=|P{|}^{4}={2}^{4}=16\)

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