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Basic Constructions

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The tools in a geometry box are:

• Ruler
• Compass
• Divider
• Set squares
• Protractor

Ruler:
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

Compass:
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 circles

Divider:
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 squares 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

Protractor:
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

Drawing a line segment of given length:

• Place the ruler on a drawing paper.
• Mark point A at the zero of the ruler.
• Count the divisions in the ruler till you reach the required length.
• Mark the point as B.
• Join points A and B.
• AB is the required line segment of length 10 cm.

Drawing a circle with a given radius:

• Drawing a circle of radius 5 cm.
• Set the compass to the desired radius, say 5 cm.
• Mark point O.
• Place the pointer end of the compass at point O.
• Make a complete round with the pencil end of the compass, keeping the pointer at the same position.
• The required circle of radius 5 cm is obtained.

1 . draw an angle of measure 153 degree

Draw an angle 60 degree and bisect 30

2 . how to draw an angle of 153 degree & 147 degree.

To draw 147°  using protractor.

First draw a line segment or a ray OA
Makre O as centre and place t...

3 . what did you mean by bisector in maths

Bisector: If a line segment is divided into two equal parts by a line then it is called a bisector of the given line segment.
Angle...