Proof

 STATEMENTS                  REASONS

 AM = CM  chords intersecting congruent arcs are congruent
 angle A = angle C  angles intercepting same arc are congruent
 AB = DC  given in construction
 triangle ABM = triangle CDM  SAS
 MB = MD  CPCTC
 triangle BMD is isosceles  Definition of isosceles triangle
 triangle BFM = triangle DFM  HL

BF = FD 

AB + BF = FD + DC

FD + DC = FC

AB + BF = FC

 CPCTC

Substition

Substitution

Substitution

RETURN