February 23, 2021

Imagine two lines that are going to intersect at a point. The point at which they intersect will create an angle. The angle is the deviation of another line from a reference. Basically, an **angle** is the region of the plane between two rays with a common origin. The rays are called **sides** and have a common origin, the **vertex**.

In the above image, the **a **and **b **are **sides **but in some textbooks, they are denoted by **arms** as well so don't get confused in terminologies, they both are the same. The **point** **O **is the **vertex **and a **vertex **is a point where both lines or planes meet each other. An angle is positive if rotated in a counterclockwise direction and negative when rotated clockwise. There are different types of angles, let's take a look at them:

## Types of Angles

### 1. Right-Angle

If the two straight lines/rays/planes (one horizontal and one vertical) meet each other, they will create a right angle. The identification of the right angle is that it will always be equal to .

### 2. Acute Angle

If the angle created by the rays/planes/lines is less than , that means you are dealing with an acute angle.

### 3. Obtuse Angle

If the angle created by the rays/planes/lines is greater than , that means the angle is an obtuse angle.

### 4. Straight Angle

If two straight lines/planes/rays (both either horizontal or vertical) meet each other, they will create a straight angle. A straight angle will always make .

### 5. Complete Angle

A complete angle is formed when two planes/rays/lines overlap each other completely hence resulting in an angle of .

### 6. Reflex Angle

If the angle is more than but less than , that means you are dealing with a reflex angle.

In addition, angles are measured in different units and each unit is very important to understand. Below are the types of units used to measure angles:

## Types of Units For Measuring Angles

### 1. Sexagesimal degree (°)

If the circumference of a circle is divided into 360 equal parts, the central angle corresponding to each of its 360 parts is an angle of one-degree sexagesimal, ().

A **degree** has **60 minutes** (') and a **minute** has **60 seconds** ('').

### 2. Radian (rad)

It is the measure of an **angle** whose **arc is a radio**.

Convert to radian.

Cross multiply:

Convert to degrees.