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Select the correct answer.

Consider matrices [tex]A[/tex] and [tex]B[/tex].
[tex]\[ A = \left[\begin{array}{cc}
-1 & 4 \\
0 & 5
\end{array}\right], \quad B = \left[\begin{array}{ccc}
7 & 9 & 2 \\
2 & 0 & -3
\end{array}\right] \][/tex]

What is the product of these matrices, [tex]AB[/tex]?

A. [tex]\(\left[\begin{array}{ccc}
1 & 9 & -14 \\
-10 & 0 & 15
\end{array}\right]\)[/tex]

B. These two matrices cannot be multiplied.

C. [tex]\(\left[\begin{array}{ccc}
1 & -9 & -14 \\
10 & 0 & -15
\end{array}\right]\)[/tex]

D. [tex]\(\left[\begin{array}{cc}
1 & -23 \\
10 & -15
\end{array}\right]\)[/tex]


Sagot :

To determine the product of matrices [tex]\( A \)[/tex] and [tex]\( B \)[/tex], we need to perform matrix multiplication.

Matrix [tex]\( A \)[/tex] has dimensions [tex]\( 2 \times 2 \)[/tex]:
[tex]\[ A = \begin{bmatrix} -1 & 4 \\ 0 & 5 \end{bmatrix} \][/tex]

Matrix [tex]\( B \)[/tex] has dimensions [tex]\( 2 \times 3 \)[/tex]:
[tex]\[ B = \begin{bmatrix} 7 & 9 & 2 \\ 2 & 0 & -3 \end{bmatrix} \][/tex]

The resulting matrix after multiplication [tex]\( AB \)[/tex] will have the dimensions [tex]\( 2 \times 3 \)[/tex] because the number of rows of [tex]\( A \)[/tex] is 2 and the number of columns of [tex]\( B \)[/tex] is 3.

We find each element of the product matrix [tex]\( AB \)[/tex] by taking the dot product of the corresponding row of [tex]\( A \)[/tex] with the column of [tex]\( B \)[/tex].

The element at position (1,1):
[tex]\[ (-1 \cdot 7) + (4 \cdot 2) = -7 + 8 = 1 \][/tex]

The element at position (1,2):
[tex]\[ (-1 \cdot 9) + (4 \cdot 0) = -9 + 0 = -9 \][/tex]

The element at position (1,3):
[tex]\[ (-1 \cdot 2) + (4 \cdot -3) = -2 + (-12) = -14 \][/tex]

The element at position (2,1):
[tex]\[ (0 \cdot 7) + (5 \cdot 2) = 0 + 10 = 10 \][/tex]

The element at position (2,2):
[tex]\[ (0 \cdot 9) + (5 \cdot 0) = 0 + 0 = 0 \][/tex]

The element at position (2,3):
[tex]\[ (0 \cdot 2) + (5 \cdot -3) = 0 + (-15) = -15 \][/tex]

Therefore, the product [tex]\( AB \)[/tex] is:
[tex]\[ AB = \begin{bmatrix} 1 & -9 & -14 \\ 10 & 0 & -15 \end{bmatrix} \][/tex]

Comparing with the options, the correct answer is:
C. [tex]\(\left[\begin{array}{ccc}1 & -9 & -14 \\ 10 & 0 & -15\end{array}\right]\)[/tex]