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