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Evaluate: [tex]\left|\begin{array}{ccc} 1 & 2 & 4 \\ 1 & 3 & 9 \\ 1 & 4 & 16 \end{array}\right|[/tex]

A. 2
B. 4
C. 8
D. 16


Sagot :

Let's find the determinant of the given matrix step-by-step.

The given matrix is:
[tex]\[ \begin{vmatrix} 1 & 2 & 4 \\ 1 & 3 & 9 \\ 1 & 4 & 16 \end{vmatrix} \][/tex]

### Step-by-Step Calculation:

1. Choose a row or a column to expand along.
To simplify our calculation, let's expand along the first row because it contains simple numbers (mostly 1's and a minor 2).

2. Apply the cofactor expansion along the first row:
[tex]\[ \text{Det} = 1 \cdot \begin{vmatrix} 3 & 9 \\ 4 & 16 \end{vmatrix} - 2 \cdot \begin{vmatrix} 1 & 9 \\ 1 & 16 \end{vmatrix} + 4 \cdot \begin{vmatrix} 1 & 3 \\ 1 & 4 \end{vmatrix} \][/tex]

3. Calculate the determinants of the 2x2 submatrices:

- For [tex]\(\begin{vmatrix} 3 & 9 \\ 4 & 16 \end{vmatrix}\)[/tex]:
[tex]\[ (3 \cdot 16) - (9 \cdot 4) = 48 - 36 = 12 \][/tex]

- For [tex]\(\begin{vmatrix} 1 & 9 \\ 1 & 16 \end{vmatrix}\)[/tex]:
[tex]\[ (1 \cdot 16) - (9 \cdot 1) = 16 - 9 = 7 \][/tex]

- For [tex]\(\begin{vmatrix} 1 & 3 \\ 1 & 4 \end{vmatrix}\)[/tex]:
[tex]\[ (1 \cdot 4) - (3 \cdot 1) = 4 - 3 = 1 \][/tex]

4. Substitute these values back into our cofactor expansion:
[tex]\[ \text{Det} = 1 \cdot 12 - 2 \cdot 7 + 4 \cdot 1 \][/tex]
Simplify:
[tex]\[ \text{Det} = 12 - 14 + 4 \][/tex]
[tex]\[ \text{Det} = 12 - 14 + 4 = 2 \][/tex]

So, the determinant of the matrix is [tex]\(2\)[/tex]. Therefore, the correct option is:

[tex]\[ \boxed{2} \][/tex]