Geometry

If you like playing with objects, or like drawing, then geometry is for you!

Geometry can be divided into:

Plane Geometry is about flat shapes like lines, circles and triangles ... shapes that can be drawn on a piece of paper

Solid Geometry is about three dimensional objects like cubes, prisms, cylinders and spheres.

Point, Line, Plane and Solid
A Point has no dimensions, only position A Line is one-dimensional A Plane is two dimensional (2D) A Solid is three-dimensional (3D)

Why?
Why do we do Geometry? To discover patterns, find areas, volumes, lengths and angles, and better understand the world around us.

Plane Geometry
Plane Geometry is all about shapes on a flat surface (like on an endless piece of paper).
 * 2D Shapes
 * Activity: Sorting Shapes
 * Triangles
 * Right Angled Triangles
 * Interactive Triangles


 * Quadrilaterals (Rhombus, Parallelogram, etc)
 * Rectangle, Rhombus, Square, Parallelogram, Trapezoid and Kite
 * Interactive Quadrilaterals
 * Parallelogram In Any Quadrilateral
 * Paper Sizes
 * Shapes Freeplay
 * Perimeter
 * Area
 * Area of Plane Shapes
 * Area Calculation Tool
 * Area of Polygon by Drawing
 * Activity: Garden Area
 * General Drawing Tool
 * Square Calculator and Rectangle Calculator

Polygons
A Polygon is a 2-dimensional shape made of straight lines. Triangles and Rectangles are polygons.

Here are some more:
 * Properties of Regular Polygons
 * Diagonals of Polygons
 * Interactive Polygons

The Circle
Circle Theorems (Advanced Topic)
 * Circle
 * Pi
 * Circle Area by Lines
 * Circle Sector and Segment
 * Circle Area by Sectors
 * Activity: Dropping a Coin onto a Grid
 * Arc
 * Annulus

Symbols
There are many special symbols used in Geometry. Here is a short reference for you:

Geometric Symbols

Congruent and Similar

 * Congruent Shapes
 * Similar Shapes

Angles
Types of Angles

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Using Drafting Tools

 * Geometric Constructions
 * Using the Protractor
 * Using the Drafting Triangle and Ruler
 * Using a Ruler and Compass
 * }
 * }

Transformations and Symmetry
Transformations: Symmetry:
 * Rotation
 * Reflection
 * Translation
 * Resizing
 * Reflection Symmetry
 * Rotational Symmetry
 * Point Symmetry
 * Lines of Symmetry of Plane Shapes
 * Symmetry Artist
 * Activity: Symmetry of Shapes
 * Activity: Make a Mandala
 * Activity: Coloring (The Four Color Theorem)
 * Tessellations
 * Tessellation Artist

Coordinates

 * Cartesian Coordinates
 * Interactive Cartesian Coordinates
 * Hit the Coordinate Game

Pythagoras

 * Pythagoras' Theorem
 * Pythagorean Triples

Conic Sections

 * Set of all points
 * Conic Sections
 * Eccentricity
 * Ellipse
 * Parabola
 * Hyperbola

Circle Theorems

 * Circle Theorems
 * Tangent and Secant Lines
 * Intersecting Secants Theorem
 * Intersecting Chords Theorem
 * Angle of Intersecting Secants Theorem

Trigonometry
Trigonometry is a special subject of its own, so you might like to visit:
 * Introduction to Trigonometry
 * Trigonometry Index

Solid Geometry
Solid Geometry is the geometry of three-dimensional space - the kind of space we live in ...

... let us start with some of the simplest shapes:

Common 3D Shapes

Polyhedra and Non-Polyhedra
There are two main types of solids, "Polyhedra", and "Non-Polyhedra":

Polyhedra (they must have flat faces): Non-Polyhedra (when any surface is not flat):
 * Polyhedron Models
 * Volume and Area of a Sphere Calculator
 * Cross Sections
 * Triangle Centers
 * Vertices, Faces, and Edges
 * Cone vs Sphere vs Cylinder
 * Pyramid vs Cone
 * Prism vs Cylinder
 * Volume of Horizontal Cylinder
 * Euler's Theorem
 * Pythagoras in 3D