Labelling Conventions

Labelling Conventions


Angles and triangles are labelled in a standard manner.

An angle is named with three letters, in capitals.

When describing an angle using the three letters A, B and C, the angle letter goes in the middle: BAC.

Triangles are labelled with three pairs of letters: a, b and c and A, B and C. The lower case letters, a, b and c represent the lengths, and the upper case letters represent the angles:

For each pair of letters, the length letters are opposite the angle letters.

Fight-angled triangles, label the right angle as C (to make sense of Pythagoras` theorem a2 + b2 = c2). The longest side of a triangle is known as the hypotenuse.


1. In a right-angled triangle, the right angle is labelled C. What is the hypotenuse labelled?

Answer: c

The hypotenuse is the name for the longest side in a right-angled triangle, and is opposite the right angle which should be labelled as C.

2. Two lines AB and CD intersect at a point, E. Give, using a three-letter label, the name of the angle shown with an x.

Answer: AED

To make the angle, work along the path A - E - D. This is written as AED.