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Geometry & Trig Reference

Math formulas, definitions, properties, diagrams and examples from Geometry and Trigonometry 

Geometry Stuff
PerimetersAreas
Circle Stuff
The Geometry of Circles: 
Definitions and formulas for the radius of a circle, the diameter of a circle, the circumference (perimeter) of a circle, the area of a circle, the chord of a circle, arc and the arc length of a circle, sector and the area of the sector of a circle
The Trigonometry of Circles:
Definitions and formulas for the arc and the arc length of a circle, sector and the area of the sector of a circle, the unit circle, the angles on the unit circle in radians, the angles on the unit circle in degrees, the points on the circumference of the unit circle
Triangle Stuff
Notations:
Geometry notations for triangles including the right triangle, congruent sides of a triangle and congruent angles of a triangle
The Geometry of Triangles:
Definitions and formulas for the area of a triangle, the sum of the angles of a triangle, the Pythagorean theorem, Pythagorean triples and special triangles (the 30-60-90 triangle and the 45-45-90 triangle)
Types of Triangles:
Definitions and formulas for triangles including right triangles, equilateral triangles, isosceles triangles, scalene triangles, obtuse triangles and acute triangles
The Trigonometry of Triangles:
Definitions and formulas for basic trigonometry, sine, cosine, tangent, cosecant, secant, cotangent, the law of sines and the law of cosines
Quadrilateral Stuff:
Definitions and formulas for perimeter and area, properties of sides and angles, diagrams
SquaresRhombuses (Rhombi)
RectanglesKites
ParallelogramsTrapezoids
Properties of Polygons:
Information on properties, interior angles and central angles
TrianglesQuadrilaterals         Pentagons
HexagonsHeptagonsOctagons
NonagonsDecagons11-gons
Dodecagons   

Properties of Polyhedra:
Information on properties, faces, edges and dihedral angles
To see all the images of the polyhedra at once, check out my Polyhedra Gallery.
 

The Five Platonic Solids

TetrahedronCubeOctahedronDodecahedronIcosahedron

The Thirteen Semi-Regular Platonic Solids

truncated
tetrahedron
truncated
cube
truncated
octahedron
truncated
dodecahedron
truncated
icosahedron

The Cubocta Family of Platonic Solids

cuboctahedronrhombicuboctahedronsnub
cuboctahedron
truncated
cuboctahedron

The Icosidodeca Family of Platonic Solids

icosidodecahedronrhombicosidodecahedronsnub
icosidodecahedron
truncated
icosidodecahedron

The Stellated Family of Platonic Solids

stellated
cuboctahedron
stellated
icosidodecahedron
small stellated
dodecahedron
great stellated
dodecahedron

  Geomentry and Trigonometry Lessons

Tessellations
Learn about tessellations and the cool artwork you can make with them

Damping Functions
These pages will explain damping functions and the very cool way they are used in music!

The Geometry of Crop Circles
Learn how to make crop circles using geometry

Interior Angles of Polygons
This lesson explains how to find the interior angles of polygons

The Pythagorean Identities
This lesson shows the derivations of the three Pythagorean Identities

What's a Limit?
This lesson explains the concept of a limit (in Calculus) from various points of view