Answered

Select the correct answer.

If [tex]$A=\left[\begin{array}{cc}-2 & 5 \\ 7 & 6\end{array}\right]$[/tex] and [tex]$|B|=-|A|$[/tex], which matrix is matrix [tex]B[/tex]?

A. [tex]$\left[\begin{array}{cc}1 & -7 \\ 6 & 3\end{array}\right]$[/tex]

B. [tex][tex]$\left[\begin{array}{ll}9 & 2 \\ 3 & 6\end{array}\right]$[/tex][/tex]

C. [tex]$\left[\begin{array}{ll}12 & 1 \\ 13 & 5\end{array}\right]$[/tex]

D. [tex]$\left[\begin{array}{cc}4 & -3 \\ 6 & 7\end{array}\right]$[/tex]



Answer :

To solve the problem, we need to determine which matrix [tex]\( B \)[/tex] gives the correct determinant relationship with matrix [tex]\( A \)[/tex].

1. Calculate the determinant of [tex]\( A \)[/tex]:
[tex]\[ A = \begin{pmatrix} -2 & 5 \\ 7 & 6 \end{pmatrix} \][/tex]
The determinant of [tex]\( A \)[/tex] is calculated as follows:
[tex]\[ \text{det}(A) = (-2 \cdot 6) - (5 \cdot 7) = -12 - 35 = -47 \][/tex]
Therefore, [tex]\(|A| = -47\)[/tex].

2. Determine the target determinant for [tex]\( B \)[/tex]:
Given that [tex]\(|B| = -|A|\)[/tex], we have:
[tex]\[ |B| = -(-47) = 47 \][/tex]

3. Check which matrix [tex]\( B \)[/tex] has a determinant of 47:

- Option A:
[tex]\[ B = \begin{pmatrix} 1 & -7 \\ 6 & 3 \end{pmatrix} \][/tex]
[tex]\[ \text{det}(B) = (1 \cdot 3) - (-7 \cdot 6) = 3 + 42 = 45 \][/tex]
This is incorrect since [tex]\( \text{det}(B) \neq 47 \)[/tex].

- Option B:
[tex]\[ B = \begin{pmatrix} 9 & 2 \\ 3 & 6 \end{pmatrix} \][/tex]
[tex]\[ \text{det}(B) = (9 \cdot 6) - (2 \cdot 3) = 54 - 6 = 48 \][/tex]
This is incorrect since [tex]\( \text{det}(B) \neq 47 \)[/tex].

- Option C:
[tex]\[ B = \begin{pmatrix} 12 & 1 \\ 13 & 5 \end{pmatrix} \][/tex]
[tex]\[ \text{det}(B) = (12 \cdot 5) - (1 \cdot 13) = 60 - 13 = 47 \][/tex]
This is correct since [tex]\( \text{det}(B) = 47 \)[/tex].

- Option D:
[tex]\[ B = \begin{pmatrix} 4 & -3 \\ 6 & 7 \end{pmatrix} \][/tex]
[tex]\[ \text{det}(B) = (4 \cdot 7) - (-3 \cdot 6) = 28 + 18 = 46 \][/tex]
This is incorrect since [tex]\( \text{det}(B) \neq 47 \)[/tex].

Therefore, the correct matrix [tex]\( B \)[/tex] is:
[tex]\[ \boxed{\begin{pmatrix} 12 & 1 \\ 13 & 5 \end{pmatrix}} \][/tex]