Để hệ vô nghiệm thì \(\dfrac{m^2}{-4}=\dfrac{1}{-1}\ne\dfrac{3m}{6}=\dfrac{m}{2}\)
=>\(\left\{{}\begin{matrix}\dfrac{m^2}{-4}=\dfrac{1}{-1}=-1\\\dfrac{m}{2}\ne-1\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}m^2=4\\m\ne-2\end{matrix}\right.\)
=>m=2