Summary Euclidean Geometry - Mathematics Grade 12 (IEB)

Euclidean geometry
Lines and angles
Angles on a straight line


1 2
B

B1 + B2 = 180°
Angles of a revolution


a c
b

a + b + c = 360°
Vertically opposite angles




Corresponding angles
(parallel lines)
x


x


Alternate angles
(parallel lines)

x

x


Co-interion angles
(parallel lines)

x

y


x + y = 180°

, Triangles
Scalene tringle




None of the sides are equal in length

Isosceles triangle




Two of the sides are equal in length
Base angles are equal

Equilateral triangle

60°




60° 60°

All the sides are equal in length
All angles = 60°

Right angled triangle




One interior angle = 90°

The sum of the interior angles of a triangle = 180°
a




b c

The exterior angle of a triangle = + of the two opposite interior angles
a




b c