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Can you find a more golden Pythagorean triangle?

Pythagorean triangle: a right triangle with integer side lengths.

Golden triangle: a right triangle whose legs are in the golden ratio.

Golden ratio: (1+√5)/2 : 1

There is no golden Pythagorean triangle because the golden ratio is irrational.

However the right triangle (a,b,c) = (262353, 424496, 499025) is almost golden because b:a = 1.6180337:1 is almost the golden ratio.

Can you find a more golden right triangle than the one just given?

Update:

Sorry, the question is meant to be about integer sided right triangles. So it should read: can you find a Pythagorean triangle more golden than (a,b,c) = (262353, 424496, 499025)? In other words with ratio of legs closer to the golden ratio than 424496/262353 = 1.6180337.

2 Answers

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  • ?
    Lv 7
    6 years ago
    Favorite Answer

    A right triagle with sides x - 1/x and 2 has hypotenuse x + 1/x (where x > 1).

    So we need to solve x - 1/x : 2 = (1 + √5)/2

    x - 1/x = 1 + √5

    x = (1+√5 + √(10 + 2√5)) / 2

    According to Wolfram Alpha, the continued fraction expansion of this is

    [3; 1, 1, 11, 1, 9, 1, 25, 1, 6, 3, 2, 3, 10, 24, 6, 133, 6, 1, 1, 3, 1, 1, 3, 12, ...]

    Letting x be the fraction generated by the first 2, 3, 4, ..., 10 of the numbers in this list,

    Then computing (x - 1/x)/2, we get

    15 / 8 ≈ 1

    45 / 28 ≈ 1.6

    3016 / 1863 ≈1.618

    7119 / 4400 ≈1.61

    700625 / 433008 ≈ 1.6180

    424496 / 262353 ≈ 1.618033

    569883075 / 352207108 ≈ 1.6180339

    614724165 / 379920428 ≈ 1.61803398

    29802502503 / 18418959496 ≈ 1.61803398

    Where (1 + sqrt(5))/2 = 1.618033988749894848204586834365638117720309179805762862135448...

    and the numerators and the denominators of the listed fractions are the sides of a Pythagorean triangle.

    Addendum

    Just for the heck of it, I let Mathematica compute

    x = FromContinuedFraction[{3,1,1,11,1 ,9,1,25,1,6, 3,2,3,10,24 ,6,133,6,1,1 ,3,1,1,3,12}]

    x = 4130493785701831 / 1173386725230941

    In which case,

    (x – 1/x)/2 = 7842071253386625780181726503540 / 4846666576791423668957241552971

    Which corresponds to the Pythagorean triangle

    (7842071253386625780181726503540,

    4846666576791423668957241552971,

    9218907660334817612551510249021)

    The difference between

    7842071253386625780181726503540 / 4846666576791423668957241552971

    And (1 + √5)/2 is

    1.598299 × 10^(-31)

  • ?
    Lv 7
    6 years ago

    What is wrong with irrational side lengths? There is indeed a Golden right triangle. The sides are 1 and φ and the hypotenuse is √(φ² + 1)

    Edit: if you mean with integral sides you are correct. One can use the continued fraction representation of φ to get as close as one pleases to a golden triangle but with the trade off of increasingly large lengths.

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