[tex]\it 3\sqrt7=\sqrt{3^2\cdot7}=\sqrt{63}<\sqrt{65} \Rightarrow3\sqrt7<\sqrt{65}\Rightarrow 3\sqrt7-\sqrt{65}<0 \Rightarrow\\ \\ \Rightarrow |3\sqrt7-\sqrt{65}|=-(3\sqrt7-\sqrt{65})=-3\sqrt7+\sqrt{65}[/tex]
