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JEE Main 20262 AprilMorning Shift
Exam
JEE Main
Year
2026
Date
2 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2026 · 2 April · Morning Shift · Mathematics · Matrices

Let A = bmatrix 1 & 2 1 & α bmatrix and B = bmatrix 3 & 3 β & 2...

Let A=[121α]A = \begin{bmatrix} 1 & 2 \\ 1 & \alpha \end{bmatrix} and B=[33β2]B = \begin{bmatrix} 3 & 3 \\ \beta & 2 \end{bmatrix}. If A2−4A+I=OA^2 - 4A + I = O and B2−5B−6I=OB^2 - 5B - 6I = O, then among the two statements :
(S1): [(B−A)(B+A)]T=[1315710][(B-A)(B+A)]^T = \begin{bmatrix} 13 & 15 \\ 7 & 10 \end{bmatrix}
and
(S2): det⁡(adj(A+B))=−5\det(\text{adj}(A+B)) = -5,

Options

  1. Aonly (S1) is correct
  2. Bonly (S2) is correct
  3. Cboth (S1) and (S2) are correct
  4. Dboth (S1) and (S2) are wrong

Correct answer

B. only (S2) is correct

Step-by-step solution

For a 2×22 \times 2 matrix MM, the characteristic equation is given by M2−Tr(M)M+det⁡(M)I=OM^2 - \text{Tr}(M)M + \det(M)I = O.

For matrix A=[121α]A = \begin{bmatrix} 1 & 2 \\ 1 & \alpha \end{bmatrix}, we are given A2−4A+I=OA^2 - 4A + I = O.
Comparing the trace, we get Tr(A)=1+α=4  ⟹  α=3\text{Tr}(A) = 1 + \alpha = 4 \implies \alpha = 3.
Thus, A=[1213]A = \begin{bmatrix} 1 & 2 \\ 1 & 3 \end{bmatrix}.

For matrix B=[33β2]B = \begin{bmatrix} 3 & 3 \\ \beta & 2 \end{bmatrix}, we are given B2−5B−6I=OB^2 - 5B - 6I = O.
Comparing the determinant, we get det⁡(B)=6−3β=−6  ⟹  3β=12  ⟹  β=4\det(B) = 6 - 3\beta = -6 \implies 3\beta = 12 \implies \beta = 4.
Thus, B=[3342]B = \begin{bmatrix} 3 & 3 \\ 4 & 2 \end{bmatrix}.

Evaluating Statement (S1):
B−A=[3342]−[1213]=[213−1]B - A = \begin{bmatrix} 3 & 3 \\ 4 & 2 \end{bmatrix} - \begin{bmatrix} 1 & 2 \\ 1 & 3 \end{bmatrix} = \begin{bmatrix} 2 & 1 \\ 3 & -1 \end{bmatrix}

B+A=[3342]+[1213]=[4555]B + A = \begin{bmatrix} 3 & 3 \\ 4 & 2 \end{bmatrix} + \begin{bmatrix} 1 & 2 \\ 1 & 3 \end{bmatrix} = \begin{bmatrix} 4 & 5 \\ 5 & 5 \end{bmatrix}

(B−A)(B+A)=[213−1][4555]=[2(4)+1(5)2(5)+1(5)3(4)−1(5)3(5)−1(5)]=[1315710](B-A)(B+A) = \begin{bmatrix} 2 & 1 \\ 3 & -1 \end{bmatrix} \begin{bmatrix} 4 & 5 \\ 5 & 5 \end{bmatrix} = \begin{bmatrix} 2(4)+1(5) & 2(5)+1(5) \\ 3(4)-1(5) & 3(5)-1(5) \end{bmatrix} = \begin{bmatrix} 13 & 15 \\ 7 & 10 \end{bmatrix}

[(B−A)(B+A)]T=[1315710]T=[1371510][(B-A)(B+A)]^T = \begin{bmatrix} 13 & 15 \\ 7 & 10 \end{bmatrix}^T = \begin{bmatrix} 13 & 7 \\ 15 & 10 \end{bmatrix}
Since [1371510]≠[1315710]\begin{bmatrix} 13 & 7 \\ 15 & 10 \end{bmatrix} \neq \begin{bmatrix} 13 & 15 \\ 7 & 10 \end{bmatrix}, Statement (S1) is incorrect.

Evaluating Statement (S2):
For any 2×22 \times 2 matrix MM, det⁡(adj(M))=det⁡(M)2−1=det⁡(M)\det(\text{adj}(M)) = \det(M)^{2-1} = \det(M).

det⁡(adj(A+B))=det⁡(A+B)\det(\text{adj}(A+B)) = \det(A+B)

det⁡(A+B)=det⁡[4555]=4(5)−5(5)=20−25=−5\det(A+B) = \det \begin{bmatrix} 4 & 5 \\ 5 & 5 \end{bmatrix} = 4(5) - 5(5) = 20 - 25 = -5

Thus, det⁡(adj(A+B))=−5\det(\text{adj}(A+B)) = -5. Statement (S2) is correct.

Therefore, only (S2) is correct.

Answer: only (S2) is correct
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