## Level 1: Stage 4

## DECAHEDRON

## !

What you need

1 octafold

1 triangle segments

The Euler formula

Here’s a simple geometry magic trick. What number would you get if you take this polyhedron, count the number of its vertices (corners), subtract the number of its edges), and add the number of its faces?

______(v) - ______(e) + ______(f) = ______

Now do this for any other polyhedron in this workbook. What number did you get?

Answer:

The result is always 2.