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Question

If each element of a matrix is zero, then the matrix is:

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
null

To determine the type of matrix in which each element is zero, let's explore the concept of matrices:

  • Null Matrix: A matrix is termed a null matrix or zero matrix if all of its elements are zero. This is the definition that best matches the description given in the question.
  • Identity Matrix: An identity matrix is a square matrix in which all the elements of the principal diagonal are ones and all other elements are zero.
  • Scalar Matrix: A scalar matrix is a diagonal matrix wherein all the elements on the diagonal are the same non-zero number, and other elements are zero.
  • Square Matrix: A matrix is a square matrix if it has the same number of rows and columns. It does not require the elements to be zero.

From the above definitions, it is clear that a matrix where each element is zero is called a null matrix.

The correct answer is: null

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Important Questions from Matrices and Determinants

  1. What is the value of the determinant of the inverse of the matrix $\begin{bmatrix} -4 & -5 \\ 2 & 2 \end{bmatrix}$?

  2. In obtaining the solution of the system of equations $x + y + z = 7$, $x + 2y+3z = 16$ and $x + 3y+4z = 22$ by Cramer's rule, the value of $y$ is obtained by dividing $D$ by $D_2$, where 

    $D = \begin{vmatrix} 1 & 1 & 1 \\ 1 & 2 & 3 \\ 1 & 3 & 4 \end{vmatrix}$ 

    What is the value of the determinant $D_2$?

  3. Consider the following in respect of non-singular matrices $A$ and $B$ : 

    I. $(AB)^{-1} = A^{-1}B^{-1}$ 

    II. $(BA)(AB)^{-1} = I$, where $I$ is the identity matrix 

    III. $(AB)^T = A^T B^T$ 

    How many of the above are correct?

  4. Consider the following statements : 

    Statement-I : 

    If $X$ is an $n \times n$ matrix, then $\det(mX) = m^n \det(X)$, where $m$ is a scalar. 

    Statement-II : 

    If $Y$ is a matrix obtained from $X$ by multiplying any row or column by a scalar $m$, then $\det(Y) = m\det(X)$. 

    Which one of the following is correct in respect of the above statements?

  5. Consider the following statements about the matrix $M = \begin{vmatrix} 71 & 23 & 48 \\ 57 & 28 & 29 \\ 65 & 17 & 48 \end{vmatrix}$ 

    Statement-I : The inverse of $M$ does not exist. 

    Statement-II : $M$ is non-singular. 

    Which one of the following is correct in respect of the above statements?

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