### Why do this
problem?

It provides experience of generalising a result from 2 dimensions
to an equivalent result in 3 dimensions. This problem asks the
question for them but learners should be encouraged to ask
themselves "What if..." and always to think about possible
generalisations.

### Key questions

What comes to mind when a problem involves squares of
distances?

If we are looking for Pythagoras theorem where are the right angles
triangles?

### Possible extension

The problem

Pythagoras for a Tetrahedron.