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Matrices · Question 5

JEE Main 2026 (Online) 2nd April Evening ShiftNumericalMedium📈 Topic in 6% papers+4
1

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 .

Answer

34

Solution

|A|=-4+8=4 0, A-1= 14 bmatrix-2&2\\-4&2 bmatrix

PA=B P=BA-1= 14 bmatrix3&9\\1&3 bmatrix bmatrix-2&2\\-4&2 bmatrix= 14 bmatrix-42&24\\-14&8 bmatrix

tr(P)= -42+84=- 172

AQ=B Q=A-1B= 14 bmatrix-2&2\\-4&2 bmatrix bmatrix3&9\\1&3 bmatrix= 14 bmatrix-4&-12\\-10&-30 bmatrix

tr(Q)= -4-304=- 172 (as expected, tr(BA-1)=tr(A-1B))

tr (2(P+Q) )=2 (- 172- 172 )=-34

Absolute value =34

Answer: 34

JEE Main 2026 (Online) 2nd April Evening Shift

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2

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

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3

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4

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6

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7

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8

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
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JEE Main 2026 (Online) 21st January Evening Shift
9

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 .

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10

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 :

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11

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 :

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