Question

The value of $x,$ if
$\left|\begin{array}{cc}2x& 5\\ 8& x\end{array}\right|=\left|\begin{array}{cc}6& 5\\ 8& 3\end{array}\right|$ is

• A. $0$
• B. $1$
• C. $2$
• D. $-3$

Answer 1

The correct option is D $-3$

$\left|\begin{array}{cc}2x& 5\\ 8& x\end{array}\right|=\left|\begin{array}{cc}6& 5\\ 8& 3\end{array}\right|$
$\Rightarrow 2x\times x-5\times 8=6\times 3-5\times 8$
$\Rightarrow 2x^2-40=18-40$
$\Rightarrow 2x^2=18$
$\Rightarrow x^2=9$
$\Rightarrow x=\pm 3$