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Question
Solve the following determinant equation:
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Solution
\[\text{ Let }∆ = \begin{vmatrix}3x - 8 & 3 & 3 \\ 3 & 3x - 8 & 3 \\ 3 & 3 & 3x - 8\end{vmatrix}\]
\[ = \begin{vmatrix}3x - 2 & 3 & 3 \\ 3x - 2 & 3x - 8 & 3 \\ 3x - 2 & 3 & 3x - 8\end{vmatrix} \left[\text{ Applying }C_1 = C_1 + C_2 + C_3 \right]\]
\[ = \left( 3x - 2 \right)\begin{vmatrix}1 & 3 & 3 \\ 1 & 3x - 8 & 3 \\ 1 & 3 & 3x - 8\end{vmatrix} \]
\[ = \left( 3x - 2 \right)\begin{vmatrix}1 & 3 & 3 \\ 0 & 3x - 11 & 0 \\ 1 & 3 & 3x - 8\end{vmatrix} \left[\text{ Applying }R_2 \text{ to }R_2 - R_1 \right]\]
\[ = \left( 3x - 2 \right)\begin{vmatrix}1 & 3 & 3 \\ 0 & 3x - 11 & 0 \\ 0 & 0 & 3x - 11\end{vmatrix} \left[\text{ Applying }R_3 \text{ to }R_3 - R_1 \right]\]
\[ ∆ = \left( 3x - 2 \right) \left( 3x - 11 \right)^2 = 0\]
\[x = \frac{2}{3}, \frac{11}{3}, \frac{11}{3}\]
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