3) [tex]\angle ADB[/tex] and [tex]\angle BDE[/tex] are supplementary (if two angles form a linear pair, they are supplementary)
4) [tex]\angle ADC[/tex] and [tex]\angle CDE[/tex] are supplementary (if two angles form a linear pair, they are supplementary)
5) [tex]\angle ADB \cong \angle ADC[/tex] (supplements of congruent angles are congruent)
6) [tex]\triangle ADB \cong \triangle ADC[/tex] (SAS)
7) [tex]\angle ABD \cong \angle ACD[/tex] (CPCTC)
