## Angles and Lines

### Notation

Two lines intersect at A. The intersection of these two lines forms an angle.

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. 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')

Angles can be measured using a protractor. ### Types of Angles

• Complementary angles add up to 90o.
• Supplementary angles add up to 180o.
• Congruent angles are equal.
• Adjacent angles are next to one another and have a common vertex and line.

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 180o Straight Between 180° and 360° Reflex ### Properties of Angles

 Property Diagram Adjacent angles on a straight line add up to 180° a + b = 180° Angles around a point add up to 360° c + d + e = 360° Vertically opposite angles are equal. f = g, h = i