Angles in Triangles
Maths: Edexcel IGCSE Higher, topic 4.1.3
Types of Triangle
There are three types of triangle: equilateral, isosceles and scalene.
Equilateral
- An equilateral triangle has all angles 60° and all sides the same length.
- It has rotational symmetry of order 3 and 3 lines of symmetry.
Isosceles
- An isosceles triangle has two sides the same length and two angles the same.
- There is one line of symmetry.
Scalene
- A scalene triangle has all sides different lengths and all angles different sizes.
Angles and Triangles
Right-angled triangle
- A right-angled triangle has one angle of 90°.
- The long side opposite the right angle is called the hypotenuse.
- Right angled triangles can be isosceles or scalene.
Obtuse- or acute-angled
- If a triangle contains an obtuse angle it is called an obtuse-angled triangle.
- If it does not, it is an acute-angled triangle.
Test yourself on Angles in Triangles
How many lines of symmetry does an isosceles triangle have?
How many equal angles does an isosceles triangle have?
How many equal lengths does an isosceles triangle have?
What is the rotational symmetry of an isosceles triangle?
What is the rotational symmetry of an equilateral triangle?