TH1: m=4
BPT sẽ là 5x+7<=0
hya x<=-7/5(loại)
TH2: m<>4
\(\text{Δ}=\left(m+1\right)^2-4\left(m-4\right)\left(2m-1\right)\)
\(=m^2+2m+1-\left(4m-16\right)\left(2m-1\right)\)
\(=m^2+2m+1-8m^2+4m+32m-16\)
\(=-7m^2+38m-15\)
Để BPT vô nghiệm thì \(\left\{{}\begin{matrix}-7m^2+38m-15< 0\\m-4>0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}7m^2-38m+15>0\\m>4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}m\in\left(-\infty;\dfrac{3}{7}\right)\cup\left(5;+\infty\right)\\m>4\end{matrix}\right.\Leftrightarrow m\in\left(5;+\infty\right)\)