Question

Let $A=\left(\begin{array}{ccc}12& 24& 5\\ x& 6& 2\\ -1& -2& 3\end{array}\right)$. The value of $x$ for which the matrix $A$ is not invertible is

• A. 6
• B. 12
• C. 3
• D. 2

Answer 1

Answer: (C)

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