The Pythagorean Theorem Calculator
The Pythagorean Theorem often called the Pythagorean equation!
The Pythagorean Theorem
In mathematics, the Pythagorean theorem, also known as Pythagoras's theorem, is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It states that the square of the hypotenuse is equal to the sum of the squares of the other two sides. The theorem can be written as an equation relating the lengths of the sides a, b and c, often called the Pythagorean equation
( a^{2} + b^{2} = c^{2} )

Pre Pythagoras
The Pythagorean theorem was known long before Pythagoras, but he may well have been the first to prove it. 
Definition
In a right angled triangle: the square of the hypotenuse is equal to the sum of the squares of the other two sides.