Answer:
[tex]m\angle ECB+m\angle EFB=180[/tex]
[tex]m\angle CDB\cong m\angle EDF[/tex]
[tex]m\angle CDB+m\angle DCB+m\angle CBD=180 \degree[/tex]
Step-by-step explanation:
From the diagram, quadrilateral BCEF is a cyclic quadrilateral.
Opposite angles if a cyclic quadrilateral sum up to 180°
[tex]m\angle ECB+m\angle EFB=180[/tex]
The diagonals intersect at D to form two pairs of vertical angles, and vertical angles are congruent.
[tex]m\angle CDB\cong m\angle EDF[/tex]
Also sum of angles in triangle CBD is 180°.
[tex]m\angle CDB+m\angle DCB+m\angle CBD=180 \degree[/tex]