Triangle is a 2D shape that has three straight sides and three vertices.
To help children visualize what these shapes look like, it’s useful to give them examples of objects in our everyday life. For instance, some traffic signs and tea bags form triangles (see the images below).
A key property of these shapes is that regardless of the type of the triangle, it has three interior angles that add up to 180°. Throughout maths lessons, pupils will learn more about these angles and how they can find missing values using this property.
What are the types of triangles?
Although all triangles have three sides and angles that add up to 180°, they can be classified into four main groups:
- equilateral triangles;
- isosceles triangles;
- scalene triangles;
- right-angled triangles.
To understand what differentiates them, let’s look at each of these types and their properties.
Equilateral Triangles
An equilateral triangle has three equal sides and three equal angles. Because all angles add up to 180°, each angle is 60°.
Isosceles Triangles
What children need to know about an isosceles triangle is that it has the following:
- Two sides, which are equal in length;
- Two interior angles, which are the same. These are called base angles.
Scalene Triangles
The properties of scalene triangles are easy to remember. These triangles have sides, which are all different in length, and interior angles, which are all different in size.
Even though all angles are different, they still add up to 180°.
Right-Angled Triangles
Finally, the fourth main type of triangle is the right-angled one. As the name suggests, these shapes have one angle, which is a right angle – it equals 90°. Pupils will also need to remember that:
- The other two angles add up to 90°;
- The longest side of this type of triangle is called the hypotenuse.
Another interesting fact about right-angled triangles is that they can be isosceles. This means that there can be a right-angled isosceles triangle.
