Mathemapedia, set up by the National Centre for Excellence in the Teaching of Maths, is a grassroots online encyclopaedia that allows users to add entries and edit existing ones.

It groups entries under headings, such as mathematical concepts, pedagogic strategies and professional strategies. Topics already covered include teaching the geometry theorem formulated by Pythagoras (above), algebra and the concept of infinity.

The centre hopes maths teachers will use Mathemapedia to collaborate and share lesson ideas.

* www.ncetm.org.uk