Pythagorean Theorem
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The Pythagorean Theorem states that for a right triangle with legs of length 
and 
and hypotenuse of length 
we have the relationship 
. This theorem has been know since antiquity and is a classic to prove; hundreds of proofs have been published and many can be demonstrated entirely visually. The Pythagorean Theorem is one of the most frequently used theorems in geometry, and is one of the many tools in a good geometer's arsenal. A very large number of geometry problems can be solved by building right triangles and applying the Pythagorean Theorem.
This is generalized by the Pythagorean Inequality and the Law of Cosines.
Introductory
Example Problems
Common Pythagorean Triples
A Pythagorean Triple is a set of 3 positive integers such that 
, i.e. the 3 numbers can be the lengths of the sides of a right triangle. Among these, the Primitive Pythagorean Triples, those in which the three numbers have no common divisor, are most interesting. A few of them are:
3-4-5
5-12-13
7-24-25
8-15-17
9-40-41
