OP ⟂ AB and OQ ⟂ CD

AP + PB = CQ + QD

Substitution

Definition

AP + AP = CQ + CQ

Algebra

OP bisects AB and OQ bisects CD

AP = CQ

Substitution

If a diameter is perpendicular to a chord, it bisects the chord

AB = AP + PB and CD = CQ + QD

Equal arcs have equal chords

AP = PB and CQ = QD

AB = CD

Given

Segment addition theorem