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Determinants · Question 24

JEE Main 2025 (Online) 7th April Morning ShiftMCQMedium📈 Topic in 42% papers+4−1
1

Let the system of equations : 2x + 3y + 5z = 9 7x + 3y - 2z = 8 12x + 3y - (4 + )z = 16 - have infinitely many solutions. Then the radius of the circle centred at ( , ) and touching the line 4x = 3y is :

  1. 75
  2. 215
  3. 7
  4. 175

Answer

(1) 75

Solution

For infinitely many solutions, = 0:

= vmatrix 2 & 3 & 5 \ 7 & 3 & -2 \ 12 & 3 & -(4 + ) vmatrix

R2 R2 - R1, R3 R3 - R1:

= vmatrix 2 & 3 & 5 \ 5 & 0 & -7 \ 10 & 0 & -(9 + ) vmatrix = -3 [-5(9 + ) + 70 ] = -3(25 - 5 )

= 0 = 5

Then eq.(2) − eq.(1): 5x - 7z = -1; eq.(3) − eq.(1): 10x - 14z = 7 -

For consistency: 7 - = 2(-1) = 9

Centre (5, 9), line 4x - 3y = 0:

r = |4(5) - 3(9)| 42 + 32 = 75

Answer: (1)

JEE Main 2025 (Online) 7th April Morning Shift

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2

The number of singular matrices of order 2, whose elements are from the set \2, 3, 6, 9\, is .

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3

Let the system of equations x + 5y - z = 1 4x + 3y - 3z = 7 24x + y + z = , R, have infinitely many solutions. Then the number of the solutions of this system, if x, y, z are integers and satisfy 7 x + y + z 77, is :

  1. 4
  2. 5
  3. 3
  4. 6
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4

If y(x) = vmatrix x & x & x+ x+1 \ 27 & 28 & 27 \ 1 & 1 & 1 vmatrix, x R, then d2ydx2 + y is equal to

  1. 28
  2. 27
  3. -1
  4. 1
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5

Let A be a matrix of order 3 3 and |A| = 5. If |2 adj(3A adj(2A))| = 2 3 5 , , , N, then + + is equal to

  1. 26
  2. 27
  3. 25
  4. 28
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6

Let I be the identity matrix of order 3 3 and for the matrix A = bmatrix & 2 & 3 \ 4 & 5 & 6 \ 7 & -1 & 2 bmatrix, |A| = -1. Let B be the inverse of the matrix adj (A adj (A2 ) ). Then |( B + I)| is equal to

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7

Let a R and A be a matrix of order 3 3 such that (A) = -4 and A + I = bmatrix 1 & a & 1 \ 2 & 1 & 0 \ a & 1 & 2 bmatrix, where I is the identity matrix of order 3 3. If ((a + 1) adj((a - 1)A)) is 2m 3n, m, n \0, 1, 2, , 20\, then m + n is equal to :

  1. 14
  2. 17
  3. 15
  4. 16
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8

If the system of linear equations 3x + y + z = 3 2x + y - z = -3 x + 2y + z = 4 has infinitely many solutions, then the value of 22 - 9 is :

  1. 31
  2. 37
  3. 43
  4. 49
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9

If the system of equations 2x + y + 3z = 5 3x + 2y - z = 7 4x + 5y + z = 9 has infinitely many solutions, then ( 2 + 2) is equal to :

  1. 30
  2. 26
  3. 22
  4. 18
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10

Let A = [aij] = bmatrix 5 128 & 4 5 \ 5 8 & 4 25 bmatrix. If Aij is the cofactor of aij, Cij = k=12 aikAjk, 1 i, j 2, and C = [Cij], then 8|C| is equal to :

  1. 288
  2. 262
  3. 222
  4. 242
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11

Let M and m respectively be the maximum and the minimum values of f(x) = vmatrix 1 + 2 x & 2 x & 4 4x \ 2 x & 1 + 2 x & 4 4x \ 2 x & 2 x & 1 + 4 4x vmatrix, x R Then M4 - m4 is equal to :

  1. 1280
  2. 1040
  3. 1215
  4. 1295
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