What is an Angle

Angles are formed by two rays or lines called the arms or sides of the angle, sharing a common endpoint, called the vertex of the angle.

Types of angles

There are various types of angles. The angles can be classified into two main types.

Basis on their measure or magnitude.

Based on the Rotaion.

Let us learn about the different types of angles in detail.

Based on measurement, angles are classified as follows.

Zero angles

Acute angles

Right angles

Obtuse angles

Straight angles

Reflex angles

Complete angles

Zero Angle: An angle with a measure of zero degrees is called a zero angle.

In other words, when two lines or two rays are in same direction with a common point called vertex, then the angle between them is zero angle.

Therefore, an angle measure zero degrees is called zero angle or zero radian.

Acute angle: An angle whose measure is less than 90º is known as Acute angle.

Simply an angle measuring between 0º and 90º.

Example: 60º, 45º, 80º are acute angles.

∠AOB in the figure is an acute angle.

Right angle: An angle whose measure is 90º is known as right angle.

In other words if an angle formed between two lines is exactly 90º then it is called a right angle.

When two lines meet at a 90º angle are called perpendicular lines.

In figure ∠AOB is a right angle. So we can say that rays OA and OB are perpendicular to each other.

Obtuse angle: An angle whose measure is greater than 90º and less than 180º is known as obtuse angle.

Simply an angle measuring between 90º and 180º is called an obtuse angle. ∠AOB in the figure is an obtuse angle.

Straight angle: An angle whose measure is 180º is known as straight angle. A straight angle is equal to two right angles.

∠AOB in the figure is a straight angle.

A straight angle is a straight line and the angle formed between two rays and two rays are opposite to each other.

Two adjacent right angles is equal to 180º.

Reflex angle: An angle whose measure is greater than 180º and less than 360º is known as reflex angle. Example: 220º, 280º, 340º are reflex angles. Simply an angle measuring between 180º and 360º is called an reflex angle.

∠AOB in the figure is a reflex angle.

Complete angle: An angle whose measure is 360º is known as complete angle. A complete angle is formed when one of the angle goes on a complete rotation a 360º.

Comparison of Angles

An angle whose degree measure is greater than another angle is a greater angle. Thus we can say that

Interior and exterior angles

In above figure ∠ABC, ∠ACB and ∠BAC are interior angles and ∠ACD is a exterior angle.