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JEE Main 20238 AprilMorning Shift
Exam
JEE Main
Year
2023
Date
8 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2023 · 8 April · Morning Shift · Mathematics · Matrices

Let [ array ll 2 1 0 array array ll 1 2 - 1 array array ll 0 - 1 2...

Let \left[210\begin{array}{ll}2 \\ 1 \\ 0\end{array}$\begin{array}{ll}1 \\ 2 \\ - 1\end{array}0−12\begin{array}{ll}0 \\ - 1 \\ 2\end{array}\right]. If \left|adj ( adj\left(adj2A )\right)\right| = ( 16{)}^{n},then, thenn$ is equal to

Options

  1. A88
  2. B1010
  3. C99
  4. D1212

Correct answer

B. 1010

Step-by-step solution

Given that A = \left[\begin{cases}2 & 1 & 0 \\ 1 & 2 & - 1 \\ 0 & - 1 & 2\end{cases}\right] and \left|adj\left(adj\left(adj2A\right)\right)\right| = {16}^{n}.</p><p>Weknowthat∣adjA∣=∣A∣n−1and.</p><p>We know that \left|adjA\right| = {\left|A\right|}^{n - 1} and\left|adj\left(adjA\right)\right| = {\left|A\right|}^{{\left(n - 1\right)}^{2}}</p><p>Similarly,∣adj(adj(adjA))∣=∣A∣(n−1)3</p><p>Similarly, \left|adj\left(adj\left(adjA\right)\right)\right| = {\left|A\right|}^{{\left(n - 1\right)}^{3}} where nn is the order of the square matrix.

Let us find \left|A\right|.</p><p>∣A∣=2(2×2−(−1)(−1))−1(1×2−0(−1))+0(1×(−1)−0×2).</p><p>\left|A\right| = 2\left(2 \times 2 - \left(- 1\right)\left(- 1\right)\right) - 1\left(1 \times 2 - 0\left(- 1\right)\right) + 0\left(1 \times \left(- 1\right) - 0 \times 2\right)

=2(3)−(2)+0=4= 2\left(3\right) - \left(2\right) + 0 = 4

⇒∣2A∣(n−1)3=∣2A∣(3−1)3⇒ {\left|2A\right|}^{{\left(n - 1\right)}^{3}} = {\left|2A\right|}^{{\left(3 - 1\right)}^{3}}

=∣2A∣8=(28)3∣A∣8= {\left|2A\right|}^{8} = {\left({2}^{8}\right)}^{3}{\left|A\right|}^{8}

⇒224×48=16n⇒ {2}^{24} \times {4}^{8} = {16}^{n}

⇒166×164=16n⇒ {16}^{6} \times {16}^{4} = {16}^{n}

⇒1610=16n⇒ {16}^{10} = {16}^{n}

⇒n=10⇒ n = 10

Therefore, the value of nn is 1010.

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