$\displaystyle{\overline{{{A}{C}}}}\usepackage{cmbright}\Huge\$ is the side opposite the $\displaystyle{{100}}^{\circ}\usepackage{cmbright}\Huge\$ angle. The corresponding side is in the same position, opposite the $\displaystyle{{100}}^{\circ}\usepackage{cmbright}\Huge\$ angle in $\displaystyle\Delta{D}{E}{F}\usepackage{cmbright}\Huge\$ .