+129852 Mmmm.....I''m not sure what "RHS" means, either...but...here's a proof
BD = CA [ diameters of a circle are equal ]
Central Angle BOA = Central Angle COD [ vertcal angles are equal ]
Chord BA = Chord CD [ equal central angles span equal chords ]
AD = AD [ reflexive property ]
So BD = CA, BA = CD and AD =AD
So...by S-S-S triangle ABD is congruent to triangle DCA
