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Quadrilateral

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In geometry, a quadrilateral is a polygon with four sides and four vertices. Quadrilaterals are further classified as follows:

  • Trapezium: two of the opposite sides are parallel.
  • Isosceles trapezium: two of the opposite sides are parallel, the two angles incident with each side are equal.
  • Parallelogram: opposite sides have equal length, opposite sides are parallel, opposite angles are equal.
  • Kite: two adjacent sides have equal length, the other two sides have equal length, opposite angles are equal.
  • Rhombus: four sides have equal length, opposite sides are parallel, opposite angles are equal.
  • Rectangle: opposite sides have equal length, opposite sides are parallel, each angle is a right angle.
  • Square (regular quadrilateral): four sides have equal length, opposite sides are parallel, each angle is a right angle.



http://www.harcourtschool.com/glossary/math/images/quadrilateral.gif

Better illustrations needed.


Also the name of a group of fortresses in Italy.