If $\left|\begin{array}{cc}3 x & 4 \\ 7 & x\end{array}\right|=\left|\begin{array}{ll}6 & 3 \\ 2 & 1\end{array}\right|$ then :
Answer & explanation
Correct answer: option 4
$\left|\begin{array}{cc}3 x & 4 \\ 7 & x\end{array}\right|=\left|\begin{array}{ll}6 & 3 \\ 2 & 1\end{array}\right| \Rightarrow(3 x)(x)-4 \times 7=6 \times 1-2 \times 3$
$\Rightarrow 3 x^2-28=6-6$
so $3 n^2=28$
$x^2=\frac{28}{3}$