1. The word 'congruent' comes from the Latin verb congruere meaning ’to come together’.
2. Euclid wrote his mathematics book, called the Elements, in Alexandria around 300 BC. In this book, he only stated three congruence tests, SSS, SAS and AAS, to which the RHS test was added later.
3. If you cut a rectangle along its diagonal, you'll get two congruent triangles and each triangle will be right angled.
4. If you cut a square along its diagonal, you'll get two congruent triangles and each triangle will be a right-angled isosceles triangle.