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

मान लीजिए \(\mathrm{a} \in \mathbf{R}\) तथा A एक \(3 \times 3\) कोटि का आव्यूह है इस प्रकार कि \(\operatorname{det}(A)=-4\) और \(A+I=\left[\begin{array}{lll}1 & a & 1 \\ 2 & 1 & 0 \\ a & 1 & 2\end{array}\right]\), जहाँ \(I\) एक \(3 \times 3\) कोटि का तत्समक आव्यूह है।
यदि \(\operatorname{det}((a+1) \operatorname{adj}((a-1) A))\) का मान \(2^m 3^n, m, n \in\) \(\{0,1,2, \ldots .20\}\) है, तो \(\mathrm{m}+\mathrm{n}\) = ___

  1. A 14
  2. B 17
  3. C 15
  4. D 16
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Correct Answer

(D) 16

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\(A = \begin{bmatrix} 1 & a & 1 \\ 2 & 1 & 0 \\ a & 1 & 2 \end{bmatrix} - I = \begin{bmatrix} 0 & a & 1 \\ 2 & 0 & 0 \\ a & 1 & 1 \end{bmatrix}\) \(\operatorname{det}(A) = 0(0-0) - a(2-0) + 1(2-0) = -2a+2\) \(-2a+2 = -4 \Rightarrow -2a = -6 \Rightarrow a=3\)…
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