Concave Angle

A concave angle is an angle that contains the extensions of its sides within itself.

Thus, a concave angle is one that measures more than 180 degrees but less than 360 degrees.

It is different from other types of angles such as acute angles (less than 90 degrees), right angles (exactly 90 degrees), obtuse angles (greater than 90 degrees but less than 180 degrees), and straight angles (exactly 180 degrees).

Note: A full angle (360 degrees) is not considered a concave angle because any segment drawn between two points within the full angle will always remain inside the angle.

Remarks

Some observations about concave angles:

• In a concave angle, you can always find at least one segment PQ between two internal points P and Q that intersects the sides "a" and "b", meaning it includes points outside the angle.
  

• A concave angle is an angle whose sides extend outward beyond 180°.

And so on.