Definition of an acute angle (one less than 90 degrees).

Definition and properties of adjacent angles - those that share a common leg or ray

Definition and properties of alternate exterior angles, showing the pairs of angles associated with a transversal

Definition and properties of alternate interior angles, showing the pairs of angles associated with a transversal

Definition of 'Angle Bisector' and a general discussion of bisection. Link to 'line bisector'

Definition of an angle.

The angle inscribed in a semicircle is always 90 degrees

Discussion of the way angles are measured in degrees, minutes, seconds.

A quick way to test your knowledge of angle types

The angle subtended by an arc at the center of the circle.

Peripheral angle: see 'inscribed angle'

Definition and properties of the central angle of a circle

From two points on a circle, the central angle is twice the inscribed angle

Definition and properties of complementary angles - two angles that add to 90 degrees

Definition of a congruent angles

Constructing 75, 105, 120, 135, 150 degree angles and more.

Definition and properties of corresponding angles, showing the pairs of corresponding angles associated with a transversal

Definition and properties of the exterior angles of a transversal

Definition of a full angle. An angle whose measure is exactly 360°.

How to construct a 30 degree angle with compass and straightedge or ruler

How to construct a 45 degree angle with compass and straightedge or ruler

How to construct a 60 degree angle with compass and straightedge or ruler

How to cosntruct a ninety degree with compass and straightedge or ruler.

How to copy an angle with compass and straightedge or ruler

An animated demonstration showing how to use a protractor to measure an angle

An animated demonstration showing how to use a protractor to draw an angle

Included definition: Angle made by two lines with a common vertex.

Definition and properties of the inscribed angle of a circle

A discussion and example of how the interior and exterior angles of a polygon are related, especially when the polygon is concave.

Definition and properties of the interior angles of a transversal

Defines what is meant by 'interior of an angle'

Definition and properties of a linear pair of angles - two angles that are adjacent and supplementary

Definition of an obtuse angle. An angle between (but not including) 90deg and 180 deg;

The exterior angles of a polygon and the method for calculating their values.

Definition of a reflex angle (one whose measure is greater than 180 degrees but less than 360 degrees).

Describes how the smallest angle is opposite the shortest side, and the largest angle is opposite the longest side.

Definition of an right angle (one whose measure is exactly 90 degrees).

Definition of a straight angle. An angle that exactly 180 degrees - a straight line.

Definition of a subtended angle - the angle created by an object at a given external point

Definition and properties of supplementary angles - two angles that add to 180 degrees

The definition and characteristics of the exterior angles of triangles

Definition and properties of vertical (or opposite) angles