4.
已知函数\(f\left( x \right)=x{\ln }x-\dfrac{1}{2}m{{x}^{2}}-x\left( m\in R \right)\).
\((1)\)若函数\(f\left( x \right)\)在\(\left( 0,+\infty \right)\)上是减函数,求实数\(m\)的取值范围;
\((2)\)若函数\(f\left( x \right)\)在\(\left( 0,+\infty \right)\)上存在两个极值点\({{x}_{1}},{{x}_{2}}\),且\({{x}_{1}} < {{x}_{2}}\),证明:\({\ln }{{x}_{1}}+{\ln }{{x}_{2}} > 2\).