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单词 PythagoreanTriplet
释义

Pythagorean triplet


A Pythagorean triplet is a set {a,b,c} of three positiveintegers such that

a2+b2=c2.

That is, {a,b,c} is a Pythagorean triplet if there exists aright triangleMathworldPlanetmath whose sides have lengths a, b, and c,respectively. For example, {3,4,5} is a Pythagorean triplet.Given one Pythagorean triplet {a,b,c}, we can produce another bymultiplying a, b, and c by the same factor k. It follows thatthere are countably many Pythagorean triplets.

Primitive Pythagorean triplets

A Pythagorean triplet is primitivePlanetmathPlanetmath if its elements arecoprimesMathworldPlanetmath. All primitive Pythagorean triplets are given by

{a=2mn,b=m2-n2,c=m2+n2,(1)

where the seed numbers m and n are any two coprime positiveintegers, one odd and one even, such tht m>n.  If one presumes of the positive integers m and n only that  m>n, one obtains also many non-primitive triplets, but not e.g. (6, 8, 10).  For getting all, one needs to multiply the right hand sides of (1) by an additional integer parametre q.

Note 1.  Among the primitive Pythagorean triples, the odd cathetusMathworldPlanetmath a may attain all odd values except 1 (set e.g.  m:=n+1) and the even cathetus b all values divisible by 4 (set  n:=1).

Note 2.  In the primitive triples, the hypothenuses c are always odd.  All possible Pythagorean hypotenuses are contraharmonic means of two different integers (and conversely).

Note 3.  N.B. that any triplet (1) is obtained from the square of a Gaussian integerMathworldPlanetmath (m+in)2 as its real partMathworldPlanetmath, imaginary part and absolute valueMathworldPlanetmathPlanetmathPlanetmath.

Note 4.  The equations (1) imply that the sum of a cathetus and the hypotenuse is always a perfect squareMathworldPlanetmath or a double perfect square.

Note 5.  One can form the sequence (cf. Sloane’s http://www.research.att.com/ njas/sequences/?q=A100686&language=english&go=SearchA100686)

1, 2, 3, 4, 7, 24, 527, 336, 164833, 354144,

taking first the seed numbers 1 and 2 which give the legs 3 and 4,taking these as new seed numbers which give the legs 7 and 24, andso on.

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更新时间:2025/5/4 16:00:55