Triplets of positive integers $x,y,z$ satisfying the Diophantine equation $x^2+y^2=z^2$. After removing a common factor, and possibly switching $x,y$, any solution $(x,y,z)$ to this equation, and consequently all Pythagorean numbers, can be obtained as $x=a^2-b^2$, $y=2ab$, $z=a^2+b^2$, where $a$ and $b$ are positive integers $(a>b)$. The Pythagorean numbers can be interpreted as the sides of a right-angled triangle (cf. Pythagoras theorem).
|[a1]||G.H. Hardy, E.M. Wright, "An introduction to the theory of numbers" , Oxford Univ. Press (1979) pp. Chapt. XIII|
Pythagorean numbers. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Pythagorean_numbers&oldid=39945