# Basic Constructions

#### Summary

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.

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#### Questions & Answers*arrow_upward*

### 1 . draw an angle of measure 153 degree

Answer.

- SME Approved

### 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...

### 4 . summative assesment 2

Soon we will be uploading these SA2 sample papers

### 5 . Prove that ∠ADC = ∠ABC.

Pl post each question individually.