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Question

For which value of x, will the matrix \(\left[ {\begin{array}{*{20}{c}} 8&x&0\\ 4&0&2\\ {12}&6&0 \end{array}} \right]\) become singular.

The correct answer is

4

Understanding Singular Matrices and Determinants

The question asks us to find the specific value of x that will make the given matrix singular. A matrix is defined as singular if its determinant is equal to zero.

Matrix Representation

The matrix provided is:

$$ 8 $$ $$ x $$ $$ 0 $$
$$ 4 $$ $$ 0 $$ $$ 2 $$
$$ 12 $$ $$ 6 $$ $$ 0 $$

Let's denote this matrix as A.

Calculating the Determinant

To find the value of x that makes the matrix singular, we first need to calculate its determinant, denoted as $ \det(A) $. We can use the cofactor expansion method. Let's expand along the first row:

$$ \det(A) = 8 \begin{vmatrix} 0 & 2 \\ 6 & 0 \end{vmatrix} - x \begin{vmatrix} 4 & 2 \\ 12 & 0 \end{vmatrix} + 0 \begin{vmatrix} 4 & 0 \\ 12 & 6 \end{vmatrix} $$

Now, we calculate the determinants of the 2x2 matrices:

  • $$ \begin{vmatrix} 0 & 2 \\ 6 & 0 \end{vmatrix} = (0 \times 0) - (2 \times 6) = 0 - 12 = -12 $$
  • $$ \begin{vmatrix} 4 & 2 \\ 12 & 0 \end{vmatrix} = (4 \times 0) - (2 \times 12) = 0 - 24 = -24 $$
  • $$ \begin{vmatrix} 4 & 0 \\ 12 & 6 \end{vmatrix} = (4 \times 6) - (0 \times 12) = 24 - 0 = 24 $$

Substitute these values back into the determinant formula:

$$ \det(A) = 8(-12) - x(-24) + 0(24) $$ $$ \det(A) = -96 + 24x + 0 $$ $$ \det(A) = -96 + 24x $$

Solving for x to Achieve Singularity

For the matrix to be singular, its determinant must be zero. So, we set $ \det(A) = 0 $:

$$ -96 + 24x = 0 $$

Now, we solve this linear equation for x:

  1. Add 96 to both sides: $$ 24x = 96 $$
  2. Divide both sides by 24: $$ x = \frac{96}{24} $$
  3. Calculate the value: $$ x = 4 $$

Therefore, the value of x that makes the matrix singular is 4.

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Important Questions from Types of Matrices

  1. If \({\rm{A}} = \left[ {\begin{array}{*{20}{c}} 1&1&{ - 1}\\ 2&{ - 3}&4\\ 3&{ - 2}&3 \end{array}} \right]{\rm{\;and\;\;B}} = \left[ {\begin{array}{*{20}{c}} { - 1}&{ - 2}&{ - 1}\\ 6&{12}&6\\ 5&{10}&5 \end{array}} \right]\) then which of the following is/are correct?

    1. A and B commute.

    2. AB is a null matrix.

    Select the correct answer using the code given below:
  2. Which one of the following matrices is an elementary matrix?

  3. The matrix  is \(\left[ {\begin{array}{c} 0&{ - 4 + i}\\ {4 + i}&0 \end{array}} \right]\)

  4. How many distinct matrices exist with all four entries taken from (1, 2)?

  5. If A and B are square matrices of order 2 such that det(AB) = det(BA), then which one of the following is correct?

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