Pythagorean Triple
Definition

A Pythagorean triple is a set of three natural numbers f, g, and h, such that f2 + g2 = h2.


Three numbers DO form a Pythagorean triple if a true result occurs when they are substituted into the Pythagorean Theorem formula.

Three numbers DO NOT form a Pythagorean triple if a false result occurs when they are substituted into the Pythagorean Theorem formula.


Usually a pythagorean triple (like the one above consisting of the natural numbers f, g and h is written as: (f, g, h).


Note also that any multiple of a Pythagorean triple is also a Pythagorean triple. For example if (f, g, h) is a Pythagorean triple, then (kf, kg, kh) [where k is any natural number] is also a Pythagorean triple.


Example One

The most common Pythagorean Triple is (3, 4, 5).

Pythagorean triple (3, 4, 5)

Note that any natural number multiple of (3, 4, 5) is a Pythagorean triple. For example consider (2x3, 2x4, 2x5) which simplifies to (6, 8, 10).

Pythagorean triple (6, 8, 10)

Example Two

The numbers 4, 5 and 6 do NOT form a pythagorean triple as no permutation of the numbers when subtituted into the Pythagorean Theorem yield a true result.

Example of three numbers which DO NOT form a Pythagorean triple

More

When a Pythagorean triple consists of natural numbers which are relatively prime, it is more properly labeled a primitive Pythagorean triple.


From the first example, consider both pythagorean triples (3, 4, 5) and (6, 8, 10).


(3, 4, 5) IS a primitive Pythagorean triple since there is no natural number (other than 1) which divides evenly into all three numbers 3, 4 and 5.

(6, 8, 10) IS NOT a primitive Pythagorean triple since the natural number 2 divides evenly into all three numbers 3, 4 and 5.


Extra

Euclid's discovered a formula for generating Pythagorean triples. Substituting the two natural numbers m and n (with m > n) into the three equations below give the Pythagorean triple (f, g, h) such that f2 + g2 = h2.


f = 2mn        g = m2 - n2        h = m2 + n2


NOTE: The Pythagorean triple generated by Euclid's formula is a primitive Pythagorean triple if and only if one of m and n are even and m and n are relatively prime.


Example One


Let m = 5 and n = 2


f = 2(5)(2)        g = 52 - 22        h = 52 + 22


Simplifying results in f = 20, g = 21 and h = 29. Notice that the numbers 20, 21 and 29 are relatively prime. Notice also that with m = 5 and n = 2, m is odd and 2 is even (one of m and n are even) and 5 > 2 (m > n).

Substituting into the Pythagorean theorem results in the following:

Example of generating three numbers which form a primitive Pythagorean triple

Example Two


Let m = 5 and n = 3


f = 2(5)(3)        g = 52 - 32        h = 52 + 32


Simplifying results in f = 30, g = 16 and h = 34. Notice that the numbers 30, 16 and 24 are NOT relatively prime, which means the the Pythagorean triple (30, 16, 34) is NOT a primitive one. Notice also that with m = 5 and n = 3, both m and n are odd (one of m and n are NOT even) and 5 > 3 (m > n).

Substituting into the Pythagorean theorem results in the following:


Example of generating three numbers which form a non-primitive Pythagorean triple