Angles

An angle is created by two rays that have a common end point, called the vertex.

The angle is also a measure of the rotation between the two rays. Angles can be measured in degrees (°) or in radians.

How to Identify an Angle

Angles are often identified using Greek letters (α, β, γ, θ, ψ). The letter theta θ is often used.

In geometric figures, points are often labelled with capital letters. Consider the angle made between points ABC, where the vertex is A and AB and AC are the rays:

The angle can be identified as the angle A, or by ∠BAC, where the middle of the 3 letters is the vertex.

How to Measure an Angle

An angle is measured by the shortest rotation between the two rays. Angles are often measure in degrees, denoted °. There are 360 degrees in a full rotation. Angles can also be measured in radians. There are 2π radians in a full rotation. Angles can be measured directly using a protractor:

Angles can also be calculated using geometry and trigonometry.

Types of Angles

The different types of angles are:

	Type of Angle	Description
	Acute	Less than 90°
	Right	90°
	Obtuse	Greater than 90° but less than 180°
	Straight	180°
	Reflex	Greater than 180°
	Full	360°

Interactive Game on the Types of Angles

Here is an interactive game to help you learn about the types of angles.

Show Instructions

Parts of an Angle

An angle is created by two rays meeting at a common endpoint, the vertex.

• A ray is a line which starts from a point.
• A vertex is the point where the two rays meet.

What's in a Name?

Angle comes from the Latin word "angulus" meaning "corner". It has the same root as the word "ankle", because the foot forms a corner with the leg.

Drag and Drop Game

Here is a drag-and-drop game to help you learn about the types of angles.

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