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  4. Let A= beginpmatrix12 24 5 x 6 2 -1 -2 3 endpmatrix. The value of x for which the matrix A is not invertible is

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Q. Let $A=\begin{pmatrix}12 & 24 & 5 \\ x & 6 & 2 \\ -1 & -2 & 3\end{pmatrix}$. The value of $x$ for which the matrix $A$ is not invertible is

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Solution:

If matrix is not invertible $\Rightarrow | A |=0$
$\therefore |A|=\begin{vmatrix} 12 & 24 & 5 \\ x & 6 & 2 \\ -1 & -2 & 3 \end{vmatrix}=0 \Rightarrow x=3$