Page 198 - Maths Class 06

14 Constructions

Introduction

Everything we see around us has a shape. Even the book you are reading has a shape. We have already
learnt about some simple shapes and how to draw them. In this chapter, we will learn about some basic
constructions liked drawing circles, line segments, perpendiculars, perpendicular-bisectors and some
special angles. For these we will use various instruments like ruler, compass, protractor, divider and set
square present in the geometry box. We have already learnt how to use ruler, divider and protractor in
earlier chapters. We shall learn about use of the rest of them in this chapter.

A compass is an instrument consisting of two arms, joined at one end. One of the arms is pointed and the
other arm has a provision to hold a pencil. It is used to draw arcs and circles and mark equal lengths.

70 80 90 100 110
60 100 80 120
50 120 110 70 60 130
40 130 50 140 Set Square
30 140 40 30 150
20 160 150 20 160
10 170 10 170 6
0 180 0 180
Protractor 5 5

4 4
Compass
3 3
2 2

1 1
9 8 7 6 5 4 3 2 1 1 2 3 4

Fig. 14.1

A triangular instrument for drawing and measuring angles is known as set square. There are two types of
set squares—one having 45°, 45° and 90° angles at the vertices and the other having 30°, 60° and 90°
angles at the vertices.

Construction of a Circle

As we have studied in the previous class that a circle is the path covered by a point which moves in such a
way that its distance from a fixed point always remains constant. The fixed point is called the centre and
the constant distance is called the ra dius of the cir cle. Hence, a cir cle can be drawn if its cen tre and ra dius
are known.

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