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Notation: labelling and naming triangles and quadrilaterals

Mathematics has its own language. It's important we understand how this language works. It uses symbols and follows rules in order to convey relevant concepts and ideas. In this way, the subject can be easily understood by everyone dealing with it.

Notation is part of mathematical language. It uses symbols and symbolic expressions to provide meaning.

Shapes and angles is an area of mathematics that is dependant upon notation.

Triangles

Vertices:

The vertices of triangles are labelled with capital letters. The example provided here shows the triangle ABC. This can also be written as ABC.

Angles

It is regular practice to label each angle using sets of three letters, having the vertex as the central letter e.g. A would usually be written as BAC or CAB.

Sides

The sides of triangles are labelled with the lower case letter of the angle immediately opposite. They may otherwise be identified using the capital letters from each end.

In the example above,
Side a (opposite A) can also be known as BC.
Side b (opposite B) can also be known as AC.
Side c (opposite C) can also be known as AB.

Types of Triangles

Quadrilaterals

Quadrilaterals are four-sided figures constructed using straight lines. They include squares, rectangles, rhombuses, parallelograms, trapeziums and kites, as well as other less regular four-sided shapes.

Vertices

Quadrilaterals are named according to the series of vertices, travelling around the shape either clockwise or anticlockwise. The vertices should be listed in successive order.

This could be quadrilateral MNOP or quadrilateral PONM, to give just 2 possible examples.

Angles

Again, it is regular practice to label each angle using sets of three letters, having the vertex as the central letter e.g. N would usually be written as MNO or ONM.

Sides

Sides are again labelled with lower case letters.


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