det [tex] \left[\begin{array}{ccc}3x&2\\-1&x\end{array}\right] [/tex] = det [tex] \left[\begin{array}{ccc}4&-2\\3&x\end{array}\right] [/tex] x = ?

[tex]
\begin{vmatrix}3x&2\\-1&x\end{vmatrix}=\begin{vmatrix}4&-2\\3&x\end{vmatrix}\\
\Leftrightarrow 3x^2-(-2)=4x-(-6)\\
\Leftrightarrow 3x^2-4x-4=0\\
\Leftrightarrow (3x+2)(x-2)=0\\
\Leftrightarrow x=-\frac{2}{3}\text{ atau }x=2
[/tex]