Properties of triangles
A triangle is a 2D shape with three sides and three angles.
The angles in a triangle add up to 180°.
The properties of different kinds of triangles are listed below.
Equilateral triangle
- all sides are of equal length - shown by the dashes on the lines
- all angles are equal (60°)
Isosceles triangle
- two sides are of equal length
- two angles are equal (called the base angles)
Scalene triangle
- the three sides are all different lengths
- none of the angles are equal
Right-angled triangle
- contains a right angle 90°
- this means the other two angles add up to 90°
- a right-angled triangle can be either isosceles or scalene
Acute-angled triangle
- all three angles are acute
- can be equilateral, isosceles or scalene
Obtuse-angled triangle
- contains an obtuse angle
- can be either isosceles or scalene
Within all triangles:
- the longest side is opposite the largest angle
- the shortest side is opposite the smallest angle
- if two, or three, angles are the same size, then the sides opposite are of equal length
