All Exams Test series for 1 year @ ₹349 only
Question

If \[ [\,x \;\; 1 \;\; 1\,] \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix} \begin{bmatrix} 1 \\ 1 \\ x \end{bmatrix} = \begin{bmatrix} 45 \end{bmatrix} \] then which one of the following is a value of \(x\)? 

This question was previously asked in
NDA 2 2025 GAT Question Paper (14-Sep-2025)
The correct answer is

1

If \[ [x \; 1 \; 1] \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix} \begin{bmatrix} 1 \\ 1 \\ x \end{bmatrix} = [45] \] then which one of the following is a value of \(x\)? \[ [x \; 1 \; 1] \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix} = [\,x+11,\; 2x+13,\; 3x+15\,] \] Now multiply with the column vector: \[ [\,x+11,\; 2x+13,\; 3x+15\,] \begin{bmatrix} 1 \\ 1 \\ x \end{bmatrix} = (x+11) + (2x+13) + (3x+15)x \] \[ = 3x^2 + 18x + 24 \] \[ 3x^2 + 18x + 24 = 45 \] \[ 3x^2 + 18x - 21 = 0 \] \[ x^2 + 6x - 7 = 0 \] \[ x = \frac{-6 \pm \sqrt{36 + 28}}{2} = \frac{-6 \pm 8}{2} \] \[ \therefore \quad x = 1 \quad \text{or} \quad x = -7 \] Final Answer: \(x = 1\) or \(x = -7\).

Was this answer helpful?

Similar Questions

  1. What is the number of different matrices, each having \(4\) entries that can be formed using \(1, 2, 3, 4\) (repetition is allowed) ?
  2. Let A be a skew-symmetric matrix of order 3.

    What is the value of det(4A4) - det(3A3) + det(2A2) - det(A) + det(-I)  where I is the identity matrix of order 3?

  3. Let A and B be symmetric matrices of same order, then which one of the following is correct regarding (AB - BA) ?

    1. Its diagonal entries are equal but nonzero

    2. The sum of its non-diagonal entries is zero

    Select the correct answer using the code given below :

  4. If \[ A = \begin{bmatrix} y & z & x \\ z & x & y \\ x & y & z \end{bmatrix} \] where \( x, y, z \) are integers, is an orthogonal matrix, then what is the value of \( x^2 + y^2 + z^2 \)?

  5. Consider the following in respect of a non-singular matrix \( M \):

    1. \( |M^2| = |M|^2 \)
    2. \( |M| = |M^{-1}| \)
    3. \( |M| = |M^T| \)

    How many of the above are correct?

  6. If \[ f(\theta) = \begin{bmatrix} \cos\theta & \sin\theta \\ -\sin\theta & \cos\theta \end{bmatrix} \] then what is \( f(\pi)^2 \) equal to?

  7. If \[ A = \begin{bmatrix} 1 & 2 & 2 \\ 2 & 1 & 2 \\ 2 & 2 & 1 \end{bmatrix} \] then what is \( A^2 - 4A \) equal to?

  8. If

    A =

    [ x y z ]
    [ y z x ]
    [ z x y ]

    where x, y, z are integers, is an orthogonal matrix, then what is A2 equal to?

  9. For what value of k is the matrix \(\begin{bmatrix} 2\cos 2\theta & 2\cos 2\theta & 6 \\ 1 -2 \sin^2\theta & 2 \cos^2\theta -1 & 3 \\ k & 2k & 1 \end{bmatrix}\)  singular?

  10. What is \([\text{adj } A]^{-1}\) equal to?

Important Questions from Matrices

  1. A generic 3 × 3 real matrix A has eigenvalues 0, 1 and 6, and I is the 3 × 3 identity matrix. The quantity/quantities that cannot be determined from this information is/are the

  2. If \(A = \(\left[ {\begin{array}{} {coshx}&{sinhx}\\ { - sinhx}&{coshx} \end{array}} \right])\) , then trace (A 2) is equal to

  3. A tansformation T: 2 → 2 first reflects points through the vertical axis (x2 - axis ) and then reflects points through the line x2 = x1. Then the standard matrix of T is:

  4. The matrix representation of T on R2 defined by T(x, y) = (2y, 3x - y) relative to the basis {(1, 3), (2, 5)} is

  5. A skew-symmetric matrix cannot be of rank

Need Expert Advice?
Test Series
NDA img
Defence
NDA 2026 Mock Test Series (Latest Pattern)
526 Tests 1 Tests Free
1164 Attempts
4.7(159)
English, Hindi

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App