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Matrices · Question 3

JEE Main 2026 (Online) 4th April Morning ShiftMCQMedium📈 Topic in 35% papers+4−1
1

Let S= \A= bmatrixa & b\ c & d bmatrix : a, b, c, d \0, 1, 2, 3, 4\ and A2-4 A+3I=0 \ be a set of 2 2 matrices. Then the number of matrices in S, for which the sum of the diagonal elements is equal to 4, is :

  1. 20
  2. 17
  3. 21
  4. 19

Answer

(4) 19

Solution

By the Cayley–Hamilton theorem, every 2 2 matrix satisfies A2-(tr A)A+( A)I=0.

With tr A=a+d=4: A2-4A+( A)I=0

Subtracting the given A2-4A+3I=0: ( A-3)I=0

ad-bc=3, and conversely every such matrix lies in S.

Now count a+d=4, ad-bc=3 with entries in \0,1,2,3,4\:

• (a,d)=(0,4) or (4,0): ad=0 bc=-3, impossible.

• (a,d)=(1,3) or (3,1): ad=3 bc=0; pairs (b,c) with bc=0: 5+5-1=9 each 18

• (a,d)=(2,2): ad=4 bc=1 b=c=1: 1 matrix

Number of matrices =18+1=19

Answer: (4)

JEE Main 2026 (Online) 4th April Morning Shift

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2

Let A= bmatrix1 & 2\ 1 & bmatrix and B= bmatrix3 & 3\ & 2 bmatrix. If A2-4A+I=0 and B2-5B-6I=0, then among the two statements: (S1) : [(B-A)(B+A) ]T= bmatrix13 & 15\ 7 & 10 bmatrix and (S2) : (adj(A+B))=-5

  1. only (S1) is correct
  2. only (S2) is correct
  3. both (S1) and (S2) are correct
  4. both (S1) and (S2) are wrong
JEE Main 2026 (Online) 2nd April Morning Shift
3

Consider the matrices A= bmatrix2 & -2\ 4 & -2 bmatrix and B= bmatrix3 & 9\ 1 & 3 bmatrix. If matrices P and Q are such that PA=B and AQ=B, then the absolute value of the sum of the diagonal elements of 2(P+Q) is .

JEE Main 2026 (Online) 2nd April Evening Shift
4

Let A, B and C be three 2 × 2 matrices with real entries such that B = (I + A)-1 and A + C = I. If BC = bmatrix 1 & -5 \ -1 & 2 bmatrix and CB bmatrix x1 \ x2 bmatrix = bmatrix 12 \ -6 bmatrix, then x1 + x2 is

  1. 4
  2. 2
  3. 0
  4. −2
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5

Let A = bmatrix 3 & -4 \ 1 & -1 bmatrix and B be two matrices such that A100 = 100B + I. Then the sum of all the elements of B100 is

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6

The number of 3 2 matrices A, which can be formed using the elements of the set \-2, -1, 0, 1, 2\ such that the sum of all the diagonal elements of ATA is 5, is

JEE Main 2026 (Online) 24th January Morning Shift
7

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

JEE Main 2026 (Online) 23rd January Evening Shift
8

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
9

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
10

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
11

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

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