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What is the determinant of the coefficient matrix of the system?

[tex]\[
\left\{
\begin{array}{l}
4x + 3y + 2z = 0 \\
-3x + y + 5z = 0 \\
-x - 4y + 3z = 0
\end{array}
\right.
\][/tex]

A. 0
B. 28
C. 130
D. 131

Sagot :

To find the determinant of the coefficient matrix of the given system of equations, follow these steps:

The system of equations is:
[tex]\[ \left\{ \begin{array}{l} 4x + 3y + 2z = 0 \\ -3x + y + 5z = 0 \\ -x - 4y + 3z = 0 \end{array} \right. \][/tex]

The coefficient matrix [tex]\( A \)[/tex] is:
[tex]\[ A = \begin{pmatrix} 4 & 3 & 2 \\ -3 & 1 & 5 \\ -1 & -4 & 3 \end{pmatrix} \][/tex]

To find the determinant of matrix [tex]\( A \)[/tex], we use the following formula for the determinant of a 3x3 matrix:
[tex]\[ \text{det}(A) = a(ei - fh) - b(di - fg) + c(dh - eg) \][/tex]
where the matrix [tex]\( A \)[/tex] is:
[tex]\[ A = \begin{pmatrix} a & b & c \\ d & e & f \\ g & h & i \end{pmatrix} \][/tex]

For our matrix [tex]\( A \)[/tex], we have:
[tex]\[ a = 4, \quad b = 3, \quad c = 2 \\ d = -3, \quad e = 1, \quad f = 5 \\ g = -1, \quad h = -4, \quad i = 3 \][/tex]

Plugging these values into the determinant formula, we get:
[tex]\[ \text{det}(A) = 4(1 \cdot 3 - 5 \cdot -4) - 3(-3 \cdot 3 - 5 \cdot -1) + 2(-3 \cdot -4 - 1 \cdot -1) \][/tex]

Simplify each term:
[tex]\[ 1 \cdot 3 - 5 \cdot -4 = 3 + 20 = 23 \\ -3 \cdot 3 - 5 \cdot -1 = -9 + 5 = -4 \\ -3 \cdot -4 - 1 \cdot -1 = 12 + 1 = 13 \][/tex]

Therefore:
[tex]\[ \text{det}(A) = 4 \cdot 23 - 3 \cdot -4 + 2 \cdot 13 \][/tex]
[tex]\[ = 92 + 12 + 26 \][/tex]
[tex]\[ = 130 \][/tex]

Thus, the determinant of the coefficient matrix is:

[tex]\[ \boxed{130} \][/tex]
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