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Find the product.

[tex]\[
\left[
\begin{array}{ccc}
-2 & 3 & 6 \\
4 & -1 & 10
\end{array}
\right]
\left[
\begin{array}{c}
-3 \\
3 \\
9
\end{array}
\right]
\][/tex]

[tex]\[
= [[?]]
\][/tex]


Sagot :

To find the product of matrix [tex]\( \mathbf{A} \)[/tex] and vector [tex]\( \mathbf{B} \)[/tex], we need to perform matrix multiplication. Here is a step-by-step process:

Given:

[tex]\[ \mathbf{A} = \begin{pmatrix} -2 & 3 & 6 \\ 4 & -1 & 10 \end{pmatrix} \][/tex]

[tex]\[ \mathbf{B} = \begin{pmatrix} -3 \\ 3 \\ 9 \end{pmatrix} \][/tex]

We want to calculate the product [tex]\( \mathbf{A} \cdot \mathbf{B} \)[/tex].

### Step-by-Step Solution:

#### Step 1: Understand the matrix dimensions
Matrix [tex]\( \mathbf{A} \)[/tex] is a [tex]\( 2 \times 3 \)[/tex] matrix, and vector [tex]\( \mathbf{B} \)[/tex] is a [tex]\( 3 \times 1 \)[/tex] matrix. Since the number of columns in [tex]\( \mathbf{A} \)[/tex] matches the number of rows in [tex]\( \mathbf{B} \)[/tex], matrix multiplication is defined.

#### Step 2: Perform multiplication
Each element of the resulting matrix (which will be a [tex]\( 2 \times 1 \)[/tex] matrix) is computed as follows:

[tex]\[ \mathbf{C} = \mathbf{A} \cdot \mathbf{B} = \begin{pmatrix} c_{11} \\ c_{21} \end{pmatrix} \][/tex]

Where each element [tex]\( c_{ij} \)[/tex] is calculated by taking the dot product of the [tex]\( i \)[/tex]-th row of [tex]\( \mathbf{A} \)[/tex] with the [tex]\( j \)[/tex]-th column of [tex]\( \mathbf{B} \)[/tex].

For [tex]\( c_{11} \)[/tex]:

[tex]\[ c_{11} = (-2 \times -3) + (3 \times 3) + (6 \times 9) \][/tex]

For [tex]\( c_{21} \)[/tex]:

[tex]\[ c_{21} = (4 \times -3) + (-1 \times 3) + (10 \times 9) \][/tex]

#### Step 3: Simplify each element
Calculate [tex]\( c_{11} \)[/tex]:

[tex]\[ c_{11} = 6 + 9 + 54 = 69 \][/tex]

Calculate [tex]\( c_{21} \)[/tex]:

[tex]\[ c_{21} = -12 - 3 + 90 = 75 \][/tex]

#### Step 4: Form the resulting product matrix

Thus, the resulting product matrix is:

[tex]\[ \mathbf{C} = \begin{pmatrix} 69 \\ 75 \end{pmatrix} \][/tex]

So the product of matrix [tex]\( \mathbf{A} \)[/tex] and vector [tex]\( \mathbf{B} \)[/tex] is:

[tex]\[ \boxed{\begin{pmatrix} 69 \\ 75 \end{pmatrix}} \][/tex]
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