Quadrilaterals

A 4-sided polygon is a quadrilateral

Polygon

Polygon is a simple closed figure made of line segments

A quadrilateral has

• 4 vertices − A, B, C, D
• 4 sides − AB, BC, CD, DA
• 4 angles − ∠A, ∠B, ∠C, ∠D

Opposite sides

• AB & CD are opposite sides
• AD & BC are opposite sides
  
  

Adjacent sides

• AB, BC are adjacent sides
• AB, AD are adjacent sides
• BC, CD are adjacent sides
• CD, DA are adjacent sides"
  

Opposite angles

• ∠A, ∠C are opposite angles
• ∠B, ∠D are opposite angles

Adjacent angles

• ∠A, ∠B are adjacent angles.
• ∠A, ∠D are adjacent angles.
• ∠B, ∠C are adjacent angles.
• ∠C, ∠D are adjacent angles.

Diagonals of a quadrilateral

Line joining two opposite vertices of a quadrilateral is a diagonal.

Here, AC, BD are diagonals of the quadrilateral.

And they meet at point O.