# Day 21: This Diagram Looks Familiar

Geometry Level 2

A cyclic quadrilateral has its sides extended and they do meet, creating the points $$E$$ and $$F$$.

As shown in the diagram, $$E$$ and $$F$$ form a circle with two of the vertices of the quadrilateral (say $$B$$ and $$D$$).

Find the angle between the lines $$EF$$ and $$AC$$.

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