What is an Angle

Angle Definition:

An angle is the figure formed by two rays meeting at a common end point called a vertex.

Write an angle using the ∠ symbol

Two rays, BA and BC intersect at vertex B to form the angle in the image

2 ways to refer to this angle:

∠ ABC
∠ B

Angle Measurement:

Angles are measured using degrees.

6 types of angles:

0° ≤ Acute Angle < 90°
Right Angle measures 90°
90° < Obtuse Angle < 180°
Straight Angle measures 180°
180° < Reflex Angle < 360°
Complete Angle measures 360°

Positive and Negative Angle Direction

Positive Angles:

Positive angles go counter-clockwise
See +α in the picture above.
This is the opposite direction that clocks go

Negative Angles:

Negative angles go counter-clockwise
See -α in the picture above.
This is the same direction that clocks go

Common Core State Standards In This Lesson

4.MD.C.5

How does the What is an Angle Calculator work?

Free What is an Angle Calculator - This lesson walks you through what an angle is and how to use it

What 3 concepts are covered in the What is an Angle Calculator?

angle: the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.
geometry: study of math dealing with shapes, space, and properties of space
what is an angle