There are **3** NRICH Mathematical resources connected to **Proof Sorting**, you may find related items under Thinking Mathematically.

Challenge Level

Take a triangular number, multiply it by 8 and add 1. What is special about your answer? Can you prove it?

Challenge Level

Can you make sense of the three methods to work out the area of the kite in the square?

Challenge Level

We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.