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Mathematics

Two matrices A and B each of order 2 x 2.

Assertion (A) : A X B = 0 ⇒ A = 0 or B = 0.

Reason (R) : Let A=[2255]A = \begin{bmatrix}[r] 2 & 2 \ 5 & 5 \end{bmatrix} ≠ 0 and B=[4343]B = \begin{bmatrix}[r] -4 & 3 \ 4 & -3 \end{bmatrix} ≠ 0 but A x B = [2255][4343]\begin{bmatrix}[r] 2 & 2 \ 5 & 5 \end{bmatrix}\begin{bmatrix}[r] -4 & 3 \ 4 & -3 \end{bmatrix} = 0.

  1. A is true, R is false.

  2. A is false, R is true.

  3. Both A and R are true and R is correct reason for A.

  4. Both A and R are true and R is incorrect reason for A.

Matrices

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Answer

It is not necessarily true in case of matrices that if A X B = 0

Then, either A = 0 or B = 0.

So, assertion (A) is false.

According to reason, A=[2255]A = \begin{bmatrix}[r] 2 & 2 \ 5 & 5 \end{bmatrix} and B=[4343]B = \begin{bmatrix}[r] -4 & 3 \ 4 & -3 \end{bmatrix}

AB=[2255].[4343]=[2×(4)+2×42×3+2×(3)5×(4)+5×45×3+5×(3)]=[8+86620+201515]=[0000]\Rightarrow AB = \begin{bmatrix}[r] 2 & 2 \ 5 & 5 \end{bmatrix}.\begin{bmatrix}[r] -4 & 3 \ 4 & -3 \end{bmatrix}\\[1em] = \begin{bmatrix}[r] 2 \times (-4) + 2 \times 4 & 2 \times 3 + 2 \times (-3)\ 5 \times (-4) + 5 \times 4 & 5 \times 3 + 5 \times (-3) \end{bmatrix}\\[1em] = \begin{bmatrix}[r] -8 + 8 & 6 - 6\ -20 + 20 & 15 - 15 \end{bmatrix}\\[1em] = \begin{bmatrix}[r] 0 & 0\ 0 & 0 \end{bmatrix}\\[1em]

So, reason (R) is true.

Hence, option 2 is the correct option.

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