proof of Pythagorean triples
If , and are positive integers such that
(1) |
then is a Pythagorean triple. If , and arerelatively prime in pairs then is a primitivePythagorean triple. Clearly, if divides any two of ,and it divides all three. And if then. That is, for a positive integer , if is a Pythagorean triple then so is .Hence, to find all Pythagorean triples, it’s sufficient to findall primitive Pythagorean triples.
Let , and be relatively prime positive integers suchthat . Set
reduced tolowest terms, That is, . From the triangle inequality. Then
(2) |
Squaring both sides of (2) and multiplying through by we get
which, after cancelling and rearranging terms, becomes
(3) |
There are two cases, either and are of opposite parity, orthey or both odd. Since , they can not both beeven.
Case 1. and of opposite parity, i.e., . So 2 divides b since is odd. From equation (2), divides .Since then , therefore alsodivides . And since , divides . Therefore. Then
(4) |
Case 2. and both odd, i.e., . So 2 divides . Then by the same processas in the first case we have
(5) |
The parametric equations in (4) and (5) appearto be different but they generate the same solutions. To showthis, let
Then , and . Substituting those values for and into (5) we get
(6) |
where , , and and are of oppositeparity. Therefore (6), with a and binterchanged, is identical to (4). Thus since, as in (4), is aprimitive Pythagorean triple, we can say that is aprimitive pythagorean triple if and only if there existsrelatively prime, positive integers and , , such that .