problem
Painting by Numbers
How many different colours of paint would be needed to paint these pictures by numbers?
How many different colours of paint would be needed to paint these pictures by numbers?
Here is a proof of Euler's formula in the plane and on a sphere together with projects to explore cases of the formula for a polygon with holes, for the torus and other solids with holes and the relationship between Euler's formula and angle deficiency of polyhedra.