## Understanding Angles

#### 1. What is an angle?

An angle is the amount of

In the figure above, lines AO and OB meet at O to make the angle AOB or

O is the

**curve**between two lines meeting or crossing at a point.**∠**is used to denote an angle.In the figure above, lines AO and OB meet at O to make the angle AOB or

**∠**AOB.O is the

**vertex**of**∠**AOB.#### 2. How do we measure angles?

Angles are measured in degrees using a protractor.

To measure the angle EFG between two lines EF and FG drawn below:

Another example:

To measure the angle EFG between two lines EF and FG drawn below:

- Place the base line of the protractor over one of the lines, say, FG.
- Place the centre of the protractor on the vertex i.e. F.
- Read the scale starting from 0° at FG to where FE crosses it. That reading is
**∠**EFG.

In our case,**∠**EFG = 55°

Another example:

#### 3. Special angles

Following are some special angles:

**Right angle**

When two lines form an angle of 90°, the angle is known as a right angle and the two lines are said to be perpendicular to each other.**Acute angle**

Angles less than 90° are acute angles.**Obtuse angle**

Angles more than 90° are obtuse angles.**Straight line**

When two lines meet at 180° they make a straight line.