## Angles and Lines 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

 Two lines intersect at A. The intersection of these two lines form angles.The angle formed is written as ∠'BAC or B C.The vertex of the angle is always represented by the middle letter. A single letter can also be used to represent an angle e.g. Â or a ### Measurement of Angles

A degree is defined as 1360th of one revolution or turn. i.e. 360° = one revolution

A minute is defined as 160th 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

 Angle size Name Examples Between 0° and 90° Acute 90° Right Between 90° and 180° Obtuse 180° Straight Between 180° and 360° Reflex ### Properties of Angles

 Adjacent angles on a straight line add up to 180°  (Adj. ∠'s on st. line are supp.) a + b = 180° Example Angles around a point add up to 360°  (∠'s at a pt. add to 360°) c + d + e = 360° Example Vertically opposite angles are equal. (Vert. opp. ∠'s equal.) f = g, h = i Example