A triangle is a polygon with three sides and three angles. It is formed by connecting three points in a flat space that are not in a straight line. These points, called vertices, are connected by straight lines, which form the sides of the triangle.
Triangles can be categorised into three types based on their sides:
Triangles can also be classified based on their angles:
We can also identify an equilateral triangle if all three angles inside the triangle are equal to each other. All angles in an equilateral triangle measure 60°.
To solve problems related to triangles, it’s important to know how to label their sides and angles.
First, label the three vertices with capital letters, such as A, B, and C.
You can represent the sides by combining the vertex letters. For example, side AB is formed by connecting vertices A and B and side BC is formed by connecting vertices B and C.
Also, you can refer to the angles by the sequence of the vertices they span. In the diagram above, the angle between lines AB and AC is labelled BAC.
Example: Identifying Types of Triangles
Classify the following triangles based on their sides and angles:
a) A triangle with sides of 3 cm, 4 cm and 5 cm.
b) A triangle with angles measuring 60°, 60° and 60°.
c) A triangle with angles measuring 90°, 45° and 45°.