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JEE Main 20266 AprilMorning Shift
Exam
JEE Main
Year
2026
Date
6 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2026 · 6 April · Morning Shift · Mathematics · Matrices

Let A = bmatrix -1 & 1 & -1 1 & 0 & 1 0 & 0 & 1 bmatrix satisfy A^2...

Let A=[−11−1101001]A = \begin{bmatrix} -1 & 1 & -1 \\ 1 & 0 & 1 \\ 0 & 0 & 1 \end{bmatrix} satisfy A2+α(adj(adj(A)))+β(adj(A)(adj(adj(A))))=[2−22−20−100−1]A^2 + \alpha(adj(adj(A))) + \beta(adj(A)(adj(adj(A)))) = \begin{bmatrix} 2 & -2 & 2 \\ -2 & 0 & -1 \\ 0 & 0 & -1 \end{bmatrix} for some α,β∈R\alpha, \beta \in \mathbb{R}. Then (α−β)2(\alpha - \beta)^2 is equal to _______

Correct answer

0

Step-by-step solution

The determinant of matrix AA is:

∣A∣=−1(0−0)−1(1−0)−1(0−0)=−1|A| = -1(0 - 0) - 1(1 - 0) - 1(0 - 0) = -1

Using the properties of the adjoint of a 3×33 \times 3 matrix:

adj(adj(A))=∣A∣3−2A=−Aadj(adj(A)) = |A|^{3-2}A = -A

adj(A)(adj(adj(A)))=adj(A)(−A)=−∣A∣I=−(−1)I=Iadj(A)(adj(adj(A))) = adj(A)(-A) = -|A|I = -(-1)I = I

The given equation simplifies to:

A2−αA+βI=[2−22−20−100−1]A^2 - \alpha A + \beta I = \begin{bmatrix} 2 & -2 & 2 \\ -2 & 0 & -1 \\ 0 & 0 & -1 \end{bmatrix}

Calculating A2A^2:

A2=[−11−1101001][−11−1101001]=[2−11−110001]A^2 = \begin{bmatrix} -1 & 1 & -1 \\ 1 & 0 & 1 \\ 0 & 0 & 1 \end{bmatrix} \begin{bmatrix} -1 & 1 & -1 \\ 1 & 0 & 1 \\ 0 & 0 & 1 \end{bmatrix} = \begin{bmatrix} 2 & -1 & 1 \\ -1 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix}

Substituting A2A^2, AA, and II into the simplified equation:

[2−11−110001]−α[−11−1101001]+β[100010001]=[2−22−20−100−1]\begin{bmatrix} 2 & -1 & 1 \\ -1 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix} - \alpha \begin{bmatrix} -1 & 1 & -1 \\ 1 & 0 & 1 \\ 0 & 0 & 1 \end{bmatrix} + \beta \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix} = \begin{bmatrix} 2 & -2 & 2 \\ -2 & 0 & -1 \\ 0 & 0 & -1 \end{bmatrix}

Comparing the corresponding elements on both sides:

From the (1,2)(1,2) element:

−1−α=−2⇒α=1-1 - \alpha = -2 \Rightarrow \alpha = 1

From the (2,2)(2,2) element:

1+β=0⇒β=−11 + \beta = 0 \Rightarrow \beta = -1

Therefore, the value of (α−β)2(\alpha - \beta)^2 is:

(1−(−1))2=22=4(1 - (-1))^2 = 2^2 = 4

Answer: 44
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