Determine whether [tex]$A=\left[\begin{array}{cc}-2 & -3 \\ 2 & -2\end{array}\right]$[/tex] and [tex]$B=\left[\begin{array}{cc}1 & -1 \\ -1 & 2\end{array}\right]$[/tex] are inverse matrices.

A. No
B. Yes



Answer :

To determine whether the matrices [tex]\( A \)[/tex] and [tex]\( B \)[/tex] are inverses of each other, we need to follow these steps:

1. Matrix Multiplication: First, compute the product of [tex]\( A \)[/tex] and [tex]\( B \)[/tex]. For two matrices to be inverses, their product must equal the identity matrix.

Given:
[tex]\[ A = \begin{pmatrix} -2 & -3 \\ 2 & -2 \end{pmatrix} \][/tex]
and
[tex]\[ B = \begin{pmatrix} 1 & -1 \\ -1 & 2 \end{pmatrix} \][/tex]

2. Compute [tex]\( AB \)[/tex]:
[tex]\[ AB = \begin{pmatrix} -2 & -3 \\ 2 & -2 \end{pmatrix} \cdot \begin{pmatrix} 1 & -1 \\ -1 & 2 \end{pmatrix} \][/tex]

To compute [tex]\( AB \)[/tex], take the dot product of rows of [tex]\( A \)[/tex] with columns of [tex]\( B \)[/tex]:

- The element in the first row and first column of [tex]\( AB \)[/tex]:
[tex]\[ (-2 \cdot 1) + (-3 \cdot -1) = -2 + 3 = 1 \][/tex]

- The element in the first row and second column of [tex]\( AB \)[/tex]:
[tex]\[ (-2 \cdot -1) + (-3 \cdot 2) = 2 - 6 = -4 \][/tex]

- The element in the second row and first column of [tex]\( AB \)[/tex]:
[tex]\[ (2 \cdot 1) + (-2 \cdot -1) = 2 + 2 = 4 \][/tex]

- The element in the second row and second column of [tex]\( AB \)[/tex]:
[tex]\[ (2 \cdot -1) + (-2 \cdot 2) = -2 - 4 = -6 \][/tex]

Thus, the product [tex]\( AB \)[/tex] is:
[tex]\[ AB = \begin{pmatrix} 1 & -4 \\ 4 & -6 \end{pmatrix} \][/tex]

3. Compare with Identity Matrix: The identity matrix for 2x2 matrices is:
[tex]\[ I = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} \][/tex]

4. Conclusion: Compare [tex]\( AB \)[/tex] with the identity matrix [tex]\( I \)[/tex]. Since:
[tex]\[ \begin{pmatrix} 1 & -4 \\ 4 & -6 \end{pmatrix} \neq \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} \][/tex]

The product [tex]\( AB \)[/tex] is not equal to the identity matrix. Therefore, matrices [tex]\( A \)[/tex] and [tex]\( B \)[/tex] are not inverse matrices.

Answer: No