Notation
Two lines intersect at A. The intersection of these two lines forms an angle.
The angle formed is written as BAC or BC.
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 ^{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')
Angles can be measured using a protractor.
Types of Angles
 Complementary angles add up to 90^{o.}
 Supplementary angles add up to 180^{o.}
 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


180^{o}

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 
