22 August 2014

Practical Geometry

Basic Constructions 

The tools in our geometry box are:

  • Ruler
  • Compass
  • Divider
  • Set squares
  • Protractor
The description of each tool and its uses are given below:


A ruler is a flat and straight-edged strip, whose one side is graduated into centimetres and the other into inches. A ruler is commonly called a scale. It is the most essential tool in geometry. It is used in all constructions.
The basic uses of a ruler are:

Measuring lengths of line segments

Drawing line segments 


A compass has two ends. One end holds a pointer, while the other end holds a pencil. It is also called a pair of compasses.

The basic uses of a compass are:
  • Marking off equal lengths
  • Drawing arcs
  • Drawing circle

A divider is a tool similar in shape to a compass. It has a pair of pointer ends.

The basic uses of a divider are:
  • Comparing lengths of line segments
  • Helping avoid positioning errors
  • Taking accurate measurements
Set squares:

The two triangular tools in the geometry box are called set squares. One of the set square is an isosceles triangle with two angles measuring 45° each. The other set square is a scalene triangle with two angles measuring 30° and 60° each. The two perpendicular sides of either set square are graduated into centimetres. 

The basic uses of set squares are:
  • Drawing perpendicular lines
  • Drawing parallel lines

A semi-circular tool with degrees marked is called a protractor. The centre of the semicircle is called the midpoint of the protractor. This point helps as a reference point for the protractor. The horizontal line is called the base line or the straight edge of the protractor. 

The basic uses of a protractor are:
  • Measuring angles
  • Drawing angles
The important points to be remembered while using the tools for construction are:
  • Draw smooth and thin lines
  • Mark points lightly
  • Maintain tools or instruments with sharp pointers and fine edges
  • Keep two pencils in the box. One is for drawing lines and marking points. The other is for using in the compass

Construction of Lines 

Construction of  Angels

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