An **angle** is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.

Unit of measurement of angle is degrees.

A circle is divided into 360 equal degrees, so that a right angle is 90°. For the time being, we will only consider angles between 0° and 360°, but later, in the section on trigonometric functions, we will consider angles greater than 360° and negative angles.

Right angle is an angle of 90°, as in a corner of a square, or formed by dividing a circle into quarters.

An angle smaller than a right angle is called an acute angle.

If an angle is larger than a right angle, but less than a straight angle, it is called an obtuse angle.

**Consider the following diagram and let us see how to measure its angle**

1. Place the protractor so that the mid point of its straight edge lies on the vertex B of the angle.

2. Adjust the protractor so that BC is along the straight-edge of the protractor.

3. There are two ‘scales’ on the protractor: read that scale which has the 0° mark coinciding with the straight-edge .

4. The mark shown by BA on the curved edge gives the degree measure of the angle. We write m ∠ABC= 40°, or simply ∠ABC= 40°.