# Iff Proof Sorter

##### Age 14 to 18Challenge Level

This proof sorter is for the problem Iff.

Can you prove that if $T$ is a triangular number, then $8T+1$ is a square number?

You can use the interactive proof sorter below to help you contruct a proof, or if you prefer you can print out these proof sorter cards, and then cut them out and rearrange them to form a proof.