Angles and triangles are labelled in a standard manner.

An angle is named with three letters, in capitals.

On the diagram above, the angle at A is labelled as BAC, with the angle letter in the middle.

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 are the angles.

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

For right-angled triangles, label the right angle as C (to make sense of Pythagoras` theorem a^{2} + b^{2} = c^{2}).

On a right-angled triangle, the longest side is known as the **hypotenuse**.

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

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).

Answer: c

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`.

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

Answer: AED

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