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Geometric Elements
Home Geometric Elements Non-Euclidean Polygon Basics Symmetry Similar/congruent Triangles Quadrilaterals Feedback Websites

 

Points

One of the most basic geometric figure is a point. All other geometric
figures are made up of a collection of points. The smallest dot you can
 mark on your paper with a sharp pencil will give you an idea of what is
 meant by a geometric point. Remember, a point is only an idea in our
mind; it is not a physical object and we regard it as having a position but
 not size or shape.

Lines

A line is the path describe by a moving point. A straight line segment is formed when we use a ruler to join two points, say A and B. We call the line segment AB or BA. A and B are called the end-points.

The diagram below shows part of lines with only one end-point and extending in only one direction. We call them rays.

A line is either straight or curved. The diagram shows a curved line. A curved line is also called a curve.

 

Planes

A plane is a flat surface in which any two points are joined by a straight line lying entirely on the surface. For example, the ceiling of a room is a horizontal plane while the wall of the room is a vertical plane.

 

  Examples of planes

 

Angles

When two rays OA and OB meet at point O, an angle is formed. O is also known as the vertex of the angle and OA and OB are the sides or arms of the angles.

( drawn with geometer's sketchpad, u can download the trial version at www.keypress.com/sketchpad )

There are many different kinds of angles. Here are a few basic ones:

An Acute angle is less than 90 degrees.

(angle B is an acute angle)

 

A right angle is equal o 90 degrees.

An obtuse angle is larger than 90 degrees but less than 180 degrees.

(Angle B is an obtuse angle )

 

A straight angle is equal to 180 degrees.

Other kinds of angles include :

Reflex angles, which are larger than 180 degrees but less than 360 degrees, complementary angles, supplementary angles etc.