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Matrices · Question 9

JEE Main 2026 (Online) 23rd January Evening ShiftNumericalMedium📈 Topic in 10% papers+4
1

Let A = bmatrix 0 & 2 & -3 \ -2 & 0 & 1 \ 3 & -1 & 0 bmatrix and B be a matrix such that B(I - A) = I + A. Then the sum of the diagonal elements of BTB is equal to

Answer

3

Solution

AT = -A, i.e. A is skew-symmetric.

|I - A| = 1 + (22 + 32 + 12) = 15 0 I - A is invertible

B = (I + A)(I - A)-1

BT = [(I - A)-1 ]T(I + A)T = (I + A)-1(I - A) ( AT = -A)

BTB = (I + A)-1(I - A)(I + A)(I - A)-1

(I - A)(I + A) = I - A2 = (I + A)(I - A)

BTB = (I + A)-1(I + A)(I - A)(I - A)-1 = I

Sum of diagonal elements of BTB = tr(I3) = 3

Answer: 3

JEE Main 2026 (Online) 23rd January Evening Shift

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2

If A = bmatrix 2 & 3 \ 3 & 5 bmatrix, then the determinant of the matrix (A2025 - 3 A2024 + A2023 ) is

  1. 12
  2. 24
  3. 28
  4. 16
JEE Main 2026 (Online) 22nd January Morning Shift
3

For some , R, let A = bmatrix & 2 \ 1 & 2 bmatrix and B = bmatrix 1 & 1 \ 1 & bmatrix be such that A2 - 4A + 2I = B2 - 3B + I = O. Then ( ( adj(A3 - B3)))2 is equal to .

JEE Main 2026 (Online) 21st January Morning Shift
4

For the matrices A = bmatrix 3 & -4 \ 1 & -1 bmatrix and B = bmatrix -29 & 49 \ -13 & 18 bmatrix, if (A15 + B) bmatrix x \ y bmatrix = bmatrix 0 \ 0 bmatrix, then among the following which one is true?

  1. x = 16, y = 3
  2. x = 5, y = 7
  3. x = 11, y = 2
  4. x = 18, y = 11
JEE Main 2026 (Online) 21st January Evening Shift
5

Let A = bmatrix & 0 & - \ 0 & 1 & 0 \ & 0 & bmatrix. If for some (0, ), A2 = AT, then the sum of the diagonal elements of the matrix (A + I)3 + (A - I)3 - 6A is equal to .

JEE Main 2025 (Online) 4th April Morning Shift
6

Let the matrix A = bmatrix 1 & 0 & 0 \ 1 & 0 & 1 \ 0 & 1 & 0 bmatrix satisfy An = An-2 + A2 - I for n 3. Then the sum of all the elements of A50 is :

  1. 44
  2. 39
  3. 52
  4. 53
JEE Main 2025 (Online) 4th April Evening Shift
7

Let A = bmatrix & -1 \ 6 & bmatrix, > 0, such that (A) = 0 and + = 1. If I denotes 2 2 identity matrix, then the matrix (I + A)8 is :

  1. bmatrix 257 & -64 \ 514 & -127 bmatrix
  2. bmatrix 766 & -255 \ 1530 & -509 bmatrix
  3. bmatrix 1025 & -511 \ 2024 & -1024 bmatrix
  4. bmatrix 4 & -1 \ 6 & -1 bmatrix
JEE Main 2025 (Online) 2nd April Morning Shift
8

Let A be a 3 3 real matrix such that A2(A - 2I) - 4(A - I) = O, where I and O are the identity and null matrices, respectively. If A5 = A2 + A + I, where , , and are real constants, then + + is equal to :

  1. 76
  2. 12
  3. 4
  4. 20
JEE Main 2025 (Online) 2nd April Evening Shift
9

Let S = \m Z : Am2 + Am = 3I - A-6 \, where A = bmatrix 2 & -1 \ 1 & 0 bmatrix. Then n(S) is equal to .

JEE Main 2025 (Online) 29th January Morning Shift
10

Let M denote the set of all real matrices of order 3 3 and let S = \-3, -2, -1, 1, 2\. Let S1 = \A = [aij] M : A = AT and aij S, i, j\, S2 = \A = [aij] M : A = -AT and aij S, i, j\, S3 = \A = [aij] M : a11 + a22 + a33 = 0 and aij S, i, j\. If n(S1 S2 S3) = 125 , then equals .

JEE Main 2025 (Online) 28th January Morning Shift
11

Let A = bmatrix 1 2 & -2 \ 0 & 1 bmatrix and P = bmatrix & - \ & bmatrix, > 0. If B = PAP , C = P B10P and the sum of the diagonal elements of C is mn, where (m, n) = 1, then m + n is :

  1. 127
  2. 2049
  3. 258
  4. 65
JEE Main 2025 (Online) 28th January Evening Shift

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