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
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
