Pythagoras’s name is given to the theorem stating that a² + b² = c² for a right triangle.
In the formula, a and b represent the lengths of the two legs meeting at the right angle, while c is the hypotenuse opposite that angle. The theorem allows a missing side to be calculated when the other two side lengths are known. For example, a triangle with legs 3 and 4 has a hypotenuse of 5.
The result was known in some form before Pythagoras, including in ancient Babylonian mathematics and Indian mathematical traditions. Nevertheless, Greek tradition associated it with Pythagoras and his school, and the theorem became part of the classical geometric canon.
Euclid later included a proof in the Elements. The theorem is used in surveying, architecture, navigation, physics, computer graphics, and distance calculations. Its converse is also useful: if the side lengths satisfy the equation, the triangle is right-angled.