Everything you need to know about triangles

Our three-sided friends, also known as Triangles, are shapes with … well obviously … three sides! Triangles have a few special properties that are useful to know, and also demonstrate how they behave.

Types

First of all let’s look at the different types of triangles. There are 4 types of triangles:

Right-angled - A triangle that has two sides that meet at a right angle

Isosceles - A triangle that has two sides of equal length

Equilateral - A triangle that has all sides of equal length

Scalene – A triangle with all sides of different length

Q1 See if you can match the pictures of the triangles to its type!

Angles

Triangles have three angles. These angles always add up to 180°. To work out a missing angle in a triangle: add the two angles you have together, and then take this away from 180.

Q2 Have a look at our example and see if you can find the missing angle in the second triangle (b)!

Area

To calculate the area of a triangle we need to use a special formula. To calculate the area (A) we use:

A = (base x height)÷2

Q3 Have a look at our example and then calculate the area of the second triangle (b)!

Top tip:

Don’t forget your units!

• Angles use degrees (°)

• Sides use centimetres (cm)

• Areas use centimetres squared (cm2)

Extension exercise:

Q4 See if you can calculate the missing height of this triangle.