Given: Circle O with diameter AB, arc AM = arc DM

Prove: △AMB ≅ △CMB

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△AMB ≅ △CMB
arc AB = 180
∠CMB = 90
Substitution
∠ABM = (1/2) * arc AM and ∠CBM = (1/2) * arc DM
∠AMB = 90
Reflexive
Given
Substitution
The angles in a linear pair are supplementary
Inscribed angle measures half its intercepted arc
Circle O with diameter AB, arc AM = arc DM
ASA (Angle-Side-Angle)
∠ABM = ∠CBM
Inscribed angle measures half its intercepted arc
MB = MB
∠AMB = (1/2) * arc AB
Definition