# Geometry & Trig Reference

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

 Geometry Stuff Perimeters Areas 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 Squares Rhombuses (Rhombi) Rectangles Kites Parallelograms Trapezoids
 Properties of Polygons:Information on properties, interior angles and central angles Triangles Quadrilaterals Pentagons Hexagons Heptagons Octagons Nonagons Decagons 11-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
 Tetrahedron Cube Octahedron Dodecahedron Icosahedron
 The Thirteen Semi-Regular Platonic Solids
 truncatedtetrahedron truncatedcube truncatedoctahedron truncateddodecahedron truncatedicosahedron
 The Cubocta Family of Platonic Solids
 cuboctahedron rhombicuboctahedron snubcuboctahedron truncatedcuboctahedron
 The Icosidodeca Family of Platonic Solids
 icosidodecahedron rhombicosidodecahedron snubicosidodecahedron truncatedicosidodecahedron
 The Stellated Family of Platonic Solids
 stellatedcuboctahedron stellatedicosidodecahedron small stellateddodecahedron great stellateddodecahedron
 Geomentry and Trigonometry LessonsTessellationsLearn about tessellations and the cool artwork you can make with themDamping FunctionsThese pages will explain damping functions and the very cool way they are used in music!The Geometry of Crop CirclesLearn how to make crop circles using geometryInterior Angles of PolygonsThis lesson explains how to find the interior angles of polygonsThe Pythagorean IdentitiesThis lesson shows the derivations of the three Pythagorean IdentitiesWhat's a Limit?This lesson explains the concept of a limit (in Calculus) from various points of view