Geometry:
Geometry is the study of basic features of basic terms like point, line, line segment, ray, plane, space, angle, solid shapes,...
Let us go through the basic geometric features of the following basic geometric terms.
Point:
A point exactly looks like a dot. There is no length or width for a point.
Point is usually named by using upper case letters.
Point has no size.
Introduction to Line, Line Segment and Ray
Line:
Line runs on either direction with no ends.
To denote that the line has no ends, put headed arrows on both sides of the line.
Example:
‹ ›
Note: Length of the line could not be measured.
Line Segment:
Consider any line and mark any two points on it, say A and B.
‹ • • ›
A B
A part of line which has both starting and ending point is called as line segment which is
represented as $\overline{AB}$
Ray:
Plot a plot A on a sheet of paper and draw a straight line with A as starting point.
• ›
A
A line which has a starting point with no end point is called as ray.
Note: Length of the ray could not be measured.
Problem:
Identify the line, line segment and ray from the following figure
MN is the line. (since it has no starting and ending point)
CD is the ray. (since it has starting point but no ending point)
AB is the line segment. (since it has starting and ending point)
Introduction to Angle
There are two rays starting from the same point moving in different direction.
The first ray is inclined to the second ray.
The particular amount of inclination is called as angle.(?1)
Angle is measured in degrees.
Degree is denoted as a small circle after the numerical value
Example:
90o, 45o, 135o
Introduction to Plane
Plane is defined as the leveled flat smooth surface.
Plane figures are those figures which are closed and has smooth leveled flat surface.
Infinite number of lines makes up the plane figures.
Since line has no starting and no ending point, the plane extends on both directions endlessly.
Plane figures boundary could be straight lines or curved lines or both.
Illustration:
 | It is a plane figure since they are closed The boundary of the plane figure is a curved line |
 | It is a plane figure since they are closed The boundaries of the plane figure have straight and curved lines. |
A A is not a plane figure. (Not closed)
B B is a plane figure. (Closed)
Introduction to Space
Space is formed by the infinite number of planes.
Any figures which are drawn in space is called 'solids'.
Example: cube, cylinder, cone ...
