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JEE Main Mathematics Matrices 2026 JEE Main 2026 (02 April Shift 1)

JEE Main Mathematics Question (2026) — Solution

Question

Let A = bmatrix 1 & 2 \\ 1 & bmatrix and B = bmatrix 3 & 3 \\ & 2 bmatrix . If A^2 - 4A + I = O and B^2 - 5B - 6I = O, then among the two statements : (S1): [(B-A)(B+A)]^T = bmatrix 13 & 15 \\ 7 & 10 bmatrix and (S2): ( adj (A+B)) = -5,

Options

  1. A. only (S1) is correct
  2. B. only (S2) is correct
  3. C. both (S1) and (S2) are correct
  4. D. both (S1) and (S2) are wrong

Answer

B. only (S2) is correct

Step-by-step solution

For a 2 2 matrix M, the characteristic equation is given by M^2 - Tr (M)M + (M)I = O. For matrix A = bmatrix 1 & 2 \\ 1 & bmatrix , we are given A^2 - 4A + I = O. Comparing the trace, we get Tr (A) = 1 + = 4 = 3. Thus, A = bmatrix 1 & 2 \\ 1 & 3 bmatrix . For matrix B = bmatrix 3 & 3 \\ & 2 bmatrix , we are given B^2 - 5B - 6I = O. Comparing the determinant, we get (B) = 6 - 3 = -6 3 = 12 = 4. Thus, B = bmatrix 3 & 3 \\ 4 & 2 bmatrix . Evaluating Statement (S1): B - A = bmatrix 3 & 3 \\ 4 & 2 bmatrix - bmatrix 1 & 2 \\ 1 & 3 bmatrix = bmatrix 2 & 1 \\ 3 & -1 bmatrix B + A = bmatrix 3 & 3 \\ 4 & 2 bmatrix + bmatrix 1 & 2 \\ 1 & 3 bmatrix = bmatrix 4 & 5 \\ 5 & 5 bmatrix (B-A)(B+A) = bmatrix 2 & 1 \\ 3 & -1 bmatrix bmatrix 4 & 5 \\ 5 & 5 bmatrix = bmatrix 2(4)+1(5) & 2(5)+1(5) \\ 3(4)-1(5) & 3(5)-1(5) bmatrix = bmatrix 13 & 15 \\ 7 & 10 bmatrix [(B-A)(B+A)]^T = bmatrix 13 & 15 \\ 7 & 10 bmatrix ^T = bmatrix 13 & 7 \\ 15 & 10 bmatrix Since bmatrix 13 & 7 \\ 15 & 10 bmatrix bmatrix 13 & 15 \\ 7 & 10 bmatrix , Statement (S1) is incorrect. Evaluating Statement (S2): For any 2 2 matrix M, ( adj (M)) = (M)^ 2-1 = (M). ( adj (A+B)) = (A+B) (A+B) = bmatrix 4 & 5 \\ 5 & 5 bmatrix = 4(5) - 5(5) = 20 - 25 = -5 Thus, ( adj (A+B)) = -5. Statement (S2) is correct. Therefore, only (S2) is correct. Answer: only (S2) is correct

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