To the limit of our ability to measure with accuracy, no right triangle has ever been measured that doesn't fit the theorem. When one is found, we'll know that the theorem is false.
This is exactly the method of science: A theory matches what we see and makes predictions that check out. When something comes along that doesn't match, we either modify the theory or completely throw it out. A theory can never be proven, but is always vulnerable to be disproven, no matter how long it has been used. All you have to do is find the example where it doesn't work, and you'll be famous.
There are over 100 of them. They can be found at //www.cut-the-knot.org/pythagoras/
Pythagoras, with alternative proofs from lots of others.
Pythagoras theorem
To know about Pythagoras theorem in detail
There are 19 various aspects of Pythagoras theorem. Pythagorean Theorem (1) Pythagoras Theorem(2) Pythagorean Theorem (3) Pythagorean Theorem (4) Pythagoras Theorem(5) Pythagorean Theorem(6) Pythagrean Theorem(7) Pythagoras Theorem(8) Pythagorean Theorem (9) Hyppocrates' lunar Minimum Distance Shortest Distance Quadrangular Pyramid (1) Quadrangular Pyramid (2) Origami Two Poles Pythagoras Tree(1) Pythagoras Tree(2) Theorem by Pappus
For a number of proofs see: http://www.cut-the-knot.org/pythagoras/ Proof 6 seems to be the most straightforward.
Pythagoras' theorem is applicable to right angle triangles
~The Pythagoras theorem
It is Pythagoras' theorem
look in google if not there, look in wikipedia. fundamental theorem of algebra and their proofs
The Pythagoras Theorem is-a mathematical equation that measures the area belonging to-a triangle.
Pythagoras invented the Pythagoras Theorem.