Calculations at a golden triangle. This is an isosceles triangle in which the length of the base and the length of one of the legs are in the ratio of the golden ratio. So there are two golden triangles. These are the golden triangle of the first kind, where the base is shorter than each of the equally long legs. In this case, the angles between base and one leg have 72 degrees and the angle opposite the base has 36 degrees. In the golden triangle of the second kind, the base is longer than each of the legs. In this case, the angles between base and one leg have 36 degrees and the angle opposite the base has 108 degrees. These two can also be called acute-angled (1st kind) and obtuse-angled (2nd kind) golden triangles. The golden triangle of the second kind is also called the golden gnomon.
Choose which of the two golden triangles you want to calculate, enter one of the two lengths and choose the number of decimal places. Then click Calculate.
Formulas:
1. kind: a = c * φ
2. kind: c = a * φ
hc = √( 4 * a² - c² ) / 4
ha = c * sin(α) = a * sin(γ)
p = 2 * a + c
A = h * c / 2
Golden ratio phi:
φ = ( 1 + √5 ) / 2 = 1.618033988749895...
Lengths, heights and perimeter have the same unit (e.g. meter), the area has this unit squared (e.g. square meter).
The golden triangle of the second kind was already described by Euclid in the Elements and its construction using compass and ruler was shown. The golden triangle of the first kind can also be constructed in this way.
Another polygon based on the golden ratio is the golden rectangle. There is only one kind of this. The golden ratio can also be found in the pentagram, in three-dimensional bodies such as the pentagonal hexecontahedron and star bodies such as the great stellated dodecahedron.
The points in the regular pentagram are golden triangles of the first kind. The triangles that are created when the inner pentagram is removed from a regular pentagon are golden triangles of the second kind. A regular decagon can be tiled together using both types of golden triangles together.