For two right-angled triangles, if an angle (other than the right angle) is the same, the third angle will also be the same. This is true because angles in a triangle add up to 180°.

Learn how to find the angles in right-angled triangles with this BBC Bitesize Maths article. For students between the ages of 11 and 14.

Many triangles in real life are not right angled. But this does not limit the use of the equation a² + b² = c² because any triangle can be cut into two right-angled ones.

The 15 rows on the tablet describe a sequence of 15 right-angle triangles, which are steadily decreasing in inclination.