A four sided polygon is a quadrilateral. It has 4 sides and 4 angles. 
We named the vertices in a cyclic manner.
This quadrilateral ABCD figure has four sides AB, BC , CD and DA. It has four angles A , B, C and D .
Quadrilateral ABCD, AB and BC are adjacent sides. 
AB and DC are opposite sides. A and C are said to be opposite angles; 
similarly, D and B are opposite angles.
Naturally A and B are adjacent angles. 


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