An angle is formed when two lines intersect at a point called the vertex.
Angles are usually measured in degrees ( ^{o} ) and minutes ( ' ), although there are other systems of measuring angles, such as radians.
Notation
Measurement of Angles
A degree is defined as ^{1}⁄_{360}th of one revolution or turn. i.e. 360° = one revolution
A minute is defined as ^{1}⁄_{60}th of a degree. i.e. 1 degree = 60 minutes (1° = 60')
Types of Angles
 Complementary angles add up to 90°
 Supplementary angles add up to 180°
 Adjacent angles are next to one another and have a common vertex and line.
 Equal angles are called congruent angles.
p and q are adjacent angles.
Angles that lie within a certain range of values are given special names
Between 0° and 90° 

90° 

180° 

Between 180° and 360° 
Properties of Angles
Adjacent angles on a straight line add up to 180° (Adj. ∠'s on st. line are supp.) 
Example  
Angles around a point add up to 360° (∠'s at a pt. add to 360°) 
Example  
Vertically opposite angles are equal. (Vert. opp. ∠'s equal.) 

Example 