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Question

Let X be a matrix of order \(3 \times 3\), Y be a matrix of order \(2 \times 3\) and Z be a matrix of order \(3 \times 2\). Which of the following statements are correct?
I. (ZY)X is defined and is a square matrix of order 3.
II. Y(XZ) is defined and is a square matrix of order 2.
III. X(YZ) is not defined.
Select the answer using the code given below.

This question was previously asked in
NDA 2 2024 GAT Question Paper (01-Sep-2024)
The correct answer is
I, II and III

Matrix Multiplication Rules Explained

To determine if a matrix product is defined, we look at the dimensions (order) of the matrices involved. If matrix A has dimensions \(m \times n\) and matrix B has dimensions \(p \times q\), their product AB is defined only if the number of columns in A (n) is equal to the number of rows in B (p). That is, \(n = p\). The resulting matrix AB will have dimensions \(m \times q\).

In this problem, we are given:

  • Matrix X has order \(3 \times 3\).
  • Matrix Y has order \(2 \times 3\).
  • Matrix Z has order \(3 \times 2\).

Let's analyze each statement based on these rules.

Statement I: (ZY)X is defined

First, consider the product ZY.

  • Z has order \(3 \times 2\).
  • Y has order \(2 \times 3\).

Since the number of columns in Z (2) equals the number of rows in Y (2), the product ZY is defined. The resulting matrix ZY has order \(3 \times 3\).

Next, consider the product (ZY)X.

  • ZY has order \(3 \times 3\).
  • X has order \(3 \times 3\).

Since the number of columns in ZY (3) equals the number of rows in X (3), the product (ZY)X is defined. The resulting matrix (ZY)X has order \(3 \times 3\). A \(3 \times 3\) matrix is a square matrix of order 3.

Therefore, statement I is correct.

Statement II: Y(XZ) is defined

First, consider the product XZ.

  • X has order \(3 \times 3\).
  • Z has order \(3 \times 2\).

Since the number of columns in X (3) equals the number of rows in Z (3), the product XZ is defined. The resulting matrix XZ has order \(3 \times 2\).

Next, consider the product Y(XZ).

  • Y has order \(2 \times 3\).
  • XZ has order \(3 \times 2\).

Since the number of columns in Y (3) equals the number of rows in XZ (3), the product Y(XZ) is defined. The resulting matrix Y(XZ) has order \(2 \times 2\). A \(2 \times 2\) matrix is a square matrix of order 2.

Therefore, statement II is correct.

Statement III: X(YZ) is not defined

First, consider the product YZ.

  • Y has order \(2 \times 3\).
  • Z has order \(3 \times 2\).

Since the number of columns in Y (3) equals the number of rows in Z (3), the product YZ is defined. The resulting matrix YZ has order \(2 \times 2\).

Next, consider the product X(YZ).

  • X has order \(3 \times 3\).
  • YZ has order \(2 \times 2\).

The number of columns in X is 3, and the number of rows in YZ is 2. Since \(3 \neq 2\), the product X(YZ) is not defined.

Therefore, statement III is correct.

Conclusion on Statements

Based on the analysis:

  • Statement I is correct.
  • Statement II is correct.
  • Statement III is correct.

Since all three statements are correct, the option including I, II, and III is the correct choice.

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Similar Questions

  1. Let \(A\) and \(B\) be matrices of order \(3 \times 3\)., If \(|A| = \frac{1}{2\sqrt{2}}\) and \(|B| = \frac{1}{729}\), then what is the value of \(|2B(\text{adj}(3A))|\)?

  2. Consider the following statements in respect of two non-singular matrices \(A\) and \(B\) of the same order \(n\):
    1. \(\text{adj}(AB) = (\text{adj}A)(\text{adj}B)\)
    2. \(\text{adj}(AB) = \text{adj}(BA)\)
    3. \((AB)\text{adj}(AB) - |AB|I_n\) is a null matrix of order \(n\)
    How many of the above statements are correct?
  3. Consider the following statements in respect of a non-singular matrix \(A\) of order \(n\):
    1. \(A(\text{adj}A^T) = A(\text{adj}A)^T\)
    2. If \(A^2 = A\), then \(A\) is identity matrix of order \(n\)
    3. If \(A^3 = A\), then \(A\) is identity matrix of order \(n\)
    Which of the statements given above are correct?
  4. Consider the following statements in respect of a skew-symmetric matrix \(A\) of order \(3\):
    1. All diagonal elements are zero.
    2. The sum of all the diagonal elements of the matrix is zero.
    3. \(A\) is orthogonal matrix.
    Which of the statements given above are correct?
  5. If $A = \begin{bmatrix} \sin 2\theta & 2 \sin^2 \theta - 1 & 0 \\ \cos 2\theta & 2 \sin \theta \cos \theta & 0 \\ 0 & 0 & 1 \end{bmatrix}$, then which of the following statements is/are correct?
    1. $A^{-1} = \text{adj}A$
    2. $A$ is skew-symmetric matrix
    3. $A^{-1} = A^T$
    Select the correct answer using the code given below :

  6. If
    \(\omega = -\frac{1}{2} + i\frac{\sqrt{3}}{2}\)
    then what is

    \(\begin{vmatrix}1 + \omega & 1 + \omega^2 & \omega + \omega^2 \\1 & \omega & \omega^2 \\\frac{1}{\omega} & \frac{1}{\omega^2} & 1\end{vmatrix}\)

    equal to?

  7. If P is a skew-symmetric matrix of order 3, then what is det(P) equal to?
  8. What is \(A(\text{adj } A)\) equal to?
  9. If \(\begin{vmatrix} a-b & p-q & x-y \\ b-c & q-r & y-z \\ c-a & r-p & z-x \end{vmatrix} = k \begin{vmatrix} a & b & c \\ p & q & r \\ x & y & z \end{vmatrix}\) then what is the value of k ?
  10. What is the value of the determinant of the inverse of the matrix \(\begin{bmatrix} -4 & -5 \\ 2 & 2 \end{bmatrix}\)?


Important Questions from Matrices and Determinants

  1. If each element of a matrix is zero, then the matrix is:
  2. Let \(A\) and \(B\) be matrices of order \(3 \times 3\)., If \(|A| = \frac{1}{2\sqrt{2}}\) and \(|B| = \frac{1}{729}\), then what is the value of \(|2B(\text{adj}(3A))|\)?

  3. Consider the following statements in respect of two non-singular matrices \(A\) and \(B\) of the same order \(n\):
    1. \(\text{adj}(AB) = (\text{adj}A)(\text{adj}B)\)
    2. \(\text{adj}(AB) = \text{adj}(BA)\)
    3. \((AB)\text{adj}(AB) - |AB|I_n\) is a null matrix of order \(n\)
    How many of the above statements are correct?
  4. Consider the following statements in respect of a non-singular matrix \(A\) of order \(n\):
    1. \(A(\text{adj}A^T) = A(\text{adj}A)^T\)
    2. If \(A^2 = A\), then \(A\) is identity matrix of order \(n\)
    3. If \(A^3 = A\), then \(A\) is identity matrix of order \(n\)
    Which of the statements given above are correct?
  5. Consider the following statements in respect of a skew-symmetric matrix \(A\) of order \(3\):
    1. All diagonal elements are zero.
    2. The sum of all the diagonal elements of the matrix is zero.
    3. \(A\) is orthogonal matrix.
    Which of the statements given above are correct?
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