In the figure below, $\displaystyle\Delta{A}{B}{C}\usepackage{cmbright}\Huge\$ ~ $\displaystyle\Delta{D}{E}{F}\usepackage{cmbright}\Huge\$ . The longest side of $\displaystyle\Delta{A}{B}{C}\usepackage{cmbright}\Huge\$ is $\displaystyle{\overline{{{A}{C}}}}\usepackage{cmbright}\Huge\$ and the shortest side is $\displaystyle{\overline{{{B}{C}}}}\usepackage{cmbright}\Huge\$ .

The length of $\displaystyle{\overline{{{A}{B}}}}\usepackage{cmbright}\Huge\$ is _____.