Introduction to Angles

A figure created by two rays coming from the same point is called an angle. The starting point or the originating point of an angle is known as the vertex. The two rays are known as arms of the angle. Symbol of angle is ∠. As shown in the figures below B is the vertex. 

The arms are AB and BC. An Angle is measured in degree. The angle may also refer to the measurement of an angle or how much rotation is carried out. The Latin term angulus, meaning corner, is the root of the math word angle. When two lines intersect, at the point of intersection and angles form. Learning about angles is most important as they form the base of geometry. 

Types of angles: Angles come in a variety of shapes and sizes in geometry. Angles are mainly divtopicIded into two parts. They are

⦁ Angles based on the magnitude

⦁ Angles based on rotation

⦁ Angles based on magnitude: 

There are seven types of angles based on the magnitudes like acute angle, obtuse angle, right angle, straight angle, zero angle, reflex angle, and complete angle. 

Let’s learn about all these angles in detail one by one: 

1) Acute Angle:  An angle whose measure is more than 0° but less than 90° is known as the acute angle. 

 For eg: 1°, 49°, 36°, 75°, 89°, etc are some examples of an acute angle. 

   2)  Obtuse Angle: The obtuse angle is defined as an angle that is greater than 90 degrees but under 180 degrees.

For eg:  91°,  95°, 115°, 150°, 175°, 179°, etc are examples of Obtuse angle. 

3) Right Angle: A angle whose exact measure is 90° is known as a right angle. The right angle is formed when two perpendicular lines meet each other. That is, one arm is facing straight up and another arm at zero degree.

4) Straight  Angle: An angle whose exact measure is 180° is known as the straight angle. It is similar to a straight line. A straight angle is nothing but a mixture of an obtuse angle and acute angle on the line.

5) Zero Angle: A zero angle is generated when the ends of arms overlap on each other or there is no angle between them.

6) Reflex  Angle: An angle whose measure goes beyond 180° but stays below 360° is known as the reflex angle.  For example 181° 201° 235° 305° 325°. If an acute angle is given we can find reflects angle. The formula is 360° minus the measurement of an acute angle. 

7) Complete Angle: A complete angle is the type of angle whose measure is exactly 360°. A complete angle is also known as a full angle. 

B) Angles based on rotation: Some of the angles are based on rotation. There are two different kinds of rotational angles. They are positive angles and negative angles.

Positive angles: The angles which are measured by anticlockwise direction is known as positive angles.

2)  Negative angles: The angles which are measured by clockwise direction is known as negative angles.