Straight Angle definition - Math Open Reference

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Straight angleAlso Flat Angle

Definition: An angle whose measure is exactly 180° - a straight line

Try this Adjust the angle below by dragging an orange dot and see how the angle ∠ABC behaves. Note that it is a Straight Angle only when it is exactly 180°

Straight (or Flat) angles are formed when the legs are pointing in exactly opposite directions. The two legs then form a single straight line through the vertex of the angle. The measure of a flat angle is thus always 180°

Types of angle

Altogether, there are six types of angle as listed below. Click on an image for a full description of that type and a corresponding interactive applet.


Acute angle Less than 90°	Right angle Exactly 90°	Obtuse angle Between 90° and 180°

Straight angle Exactly 180°	Reflex angle Between 180° and 360°	Full angle Exactly 360°

Types of angle

Related angle topics

General

Angle Types

Angle relationships