The diagram shows a scalene triangle with side lengths 13 cm, 21 cm and 20 cm.

From a point O inside the triangle, line segments can be drawn at right angles to each of the sides.

The lengths of these line segments are 9 cm, 3 cm and 3.6 cm, as shown in the diagram.

What is the area of the triangle?

You can find more short problems, arranged by curriculum topic, in our short problems collection.