Quadrilateral

Definition

A quadrilateral is a four-sided polygon.

Types of quadrilaterals

Kite

Main article: Kite

A kite is a quadrilateral with two pairs of adjacent congruent edges.

Cyclic Quadrilateral

Main article: Cyclic quadrilateral

A cyclic quadrilateral is a quadrilateral that is cyclic.

Parallelogram

Main article: Parallelogram

A parallelogram is a quadrilateral with two pairs of parallel edges.

Rhombus

Main article: Rhombus

A rhombus is an equilateral parallelogram.

Rectangle

Main article: Rectangle

A rectangle is an equiangular parallelogram.

Square

Main article: Square (geometry)

A square is any figure that is both a rectangle and a rhombus.

Introductory topics

• Cyclic quadrilaterals

Resources

Books

• Introduction to Geometry by Richard Rusczyk

Intermediate topics

• Ptolemy's Theorem
• Brahmagupta's formula

Resources

Books

• Challenging Problems in Geometry -- A good book for students who already have a solid handle on elementary geometry.
• Geometry Revisited -- A classic.

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