Angles created by intersection of diameters in a circle

Angles created by intersection of diameters
Angles in intersection of diameters

The intersection creates 4 equal radii AO, CO, DO and BO.
The intersection point O is at the center of the circle and it divides each diameter to 2 radii: the diameter AB is divided to radii AO and OB; the diameter CD is divided to radii CO and OD.
The intersection creates 4 central angles: ∠COA, ∠AOD, ∠DOB and ∠BOC.
The intersection creates 2 pairs of equal vertical angles: ∠COA=∠BOD; ∠COB=∠AOD.
The intersection creates 4 pairs of supplementary angles: ∠COA+∠AOD=180°; ∠AOD+∠DOB=180°; ∠DOB+∠BOC=180°; ∠BOC+∠COA=180°.

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