Page 74 - Start Up Mathematics_6

4 Basic Geometric Concepts

Geometry is a branch of Mathematics which deals with the study of shape, size and relative position
of figures. In ancient times, people used geometry in several ways which includes surveying land
areas, measuring storage containers, constructing, palaces, temples etc. Eventually it was realized
that geometry is not restricted to the study of plane surfaces but it is reflected in any form of art,
measurement, architecture, etc.

The word geometry is derived from two Greek words geo meaning Earth and metron meaning
measurement. Geometry has come a long way from the time of its first systematic study by Euclid
to the recent times.
In this chapter, we will learn about the fundamental building blocks of geometry i.e., points, lines
and planes. Besides this we will study basic concepts of other geometrical entities such as line
segments, rays, curves, polygons, angles, triangles, quadrilaterals, circles, parts of a circle, etc.

Point
A point is a mark of position. It determines a location. A small dot which is invisibly thin represents
a point. Points are denoted by capital letters like A, P, etc.

Some practical examples of point are as follows:

Pencil with a sharp end Tip of a compass Pointed end of a pin Tip of a cone
A point has no length, breadth or thickness, i.e., it has no dimensions.

Line
A collection of points along an endless straight path is called a
line. It has no beginning and no end. It is represented by two P Q
points on it, as shown in the figure:

The arrows on both sides show that the line is endless. It is denoted by PQ or PQ or small letters
l, m, etc.

Line Segment
A part of a line from one fixed point to the other is called a line
segment. In the adjoining figure, a line segment denoted by AB A B
or BA is shown.

• A line has length but no width.
• A line segment has a definite length which can be measured.