What Is Ptolemy’s Hypothesis?

Ptolemy’s hypothesis states, ‘For any cyclic quadrilateral, the result of its diagonals is equivalent to the amount of the result of each sets of inverse sides. The hypothesis can be additionally reached out to demonstrate the connection between the sides of a pentagon and its corner to corner, the Brilliant Proportion, and the Pythagorean hypothesis, in addition to other things.

Have you at any point considered what Michelangelo’s Sacred Family, a man engraved in a pentagram by Henrique Agrippa, and The Last Dinner by Salvador Dali share practically speaking?

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Aside from being immortal creative wonders, they all follow a typical plan reasoning/component. Each has the type of a pentagon, and the proportion of any standard pentagon side to its inclining gives the ‘brilliant proportion’ (1.618033… ). Man-caused developments and regular items that to follow the brilliant proportion in their development are viewed as the most tastefully satisfying things on the planet.

This tasteful connection between the diagonals and sides of a pentagon can be demonstrated by broadening Plotmy’s hypothesis of cyclic quadrilaterals. Additionally, Ptolemy’s hypothesis can be utilized to demonstrate the Pythagorean hypothesis also, yet before we get to all that, what is Ptolemy’s hypothesis?

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Ptolemy’s Hypothesis

The brilliant proportion connection between the sides and diagonals of a pentagon has been involved throughout the long term in numerous well known craftsmanships.

What is the Fibonacci Arrangement and the Brilliant Proportion? Straightforward clarification and models in day to day existence

Ptolemy’s hypothesis

Claudius Ptolemy was a Greek legend with mastery in a few regions; While he was generally famous for his work in cosmology (the Ptolemaic framework), he was likewise a significant math entertainer and found a hypothesis currently known as ‘Ptolemy’s hypothesis’. The hypothesis was referenced in Section 10 of Book 1 of Ptolemy’s Almagest and relates the four sides of a cyclic quadrilateral (a quadrilateral with each of the four vertices on a circle) to its diagonals.

Ptolemy’s hypothesis states, ‘For a quadrilateral engraved all around, the amount of the result of each sets of inverse sides is equivalent to the result of its two diagonals.

Think about a quadrilateral ABCD, whose vertices, i.e., A, B, C, D lie on a circle, hence shaping a cyclic quadrilateral. Here, AC and BD are the diagonals of a quadrilateral, while any remaining line fragments (Stomach muscle, BC, Disc, Promotion) are its sides. Presently as indicated by Ptolemy’s hypothesis, the amount of the result of inverse sides (Stomach muscle × Disc + BC × Promotion) is equivalent to the result of the diagonals (AC × BD).


AC × BD = (Stomach muscle × Cd) + (BC × Promotion)

Ptolemy Relationship

Cyclic quadrilateral ABCD (Photograph Credits: Kmhkmh/Wikimedia Center)

There are numerous techniques by which the above connection and in this way the hypothesis has been demonstrated throughout the long term. A few mathematicians utilize geometrical personalities to demonstrate connections, while others utilize complex numbers or opposite calculation. In any case, the easiest (as per us) of all verifications is given by the utilization of comparable triangles and their properties.

Like pretty much every numerical confirmation, we start by expecting something.

For the above cyclic quadrilateral, there is a point K on the corner to corner AC to such an extent that ABK = CBD.

Ptolemy’s hypothesis

As found in the above outline, circular segment BC meets BAC and BDC and as per the engraved point hypothesis, BAC = BDC. Additionally, circular segment Stomach muscle subtends ADB and ACB, so the two points are equivalent (∠ADB = ACB). As indicated by the Point (AA) Hypothesis of Comparable Triangles, ABK is like DBC and KBC is like ABD.

For Comparative Triangles Abk And Dbc:

Frac {Ak} {Ab} = Frac {Dc} {Db}

Along these lines, AK.DB = AB.DC

Also, for comparable triangles KBC and ABD:

frac {kc} {bc} = frac {ad} {bd}

Along these lines, KC.BD = BC.AD

Adding the above conditions, we have:


Here, dB and BD are something very similar and should be possible as a typical multiplier,

(AK + KC).BD = AB.DC + BC.AD

From the chart, AK + KC = AC.



He remained The result of the diagonals of a cyclic quadrilateral ABCD is equivalent to the amount of the result of its contrary sides, as Ptolemy’s hypothesis tells us!

Uses of Ptolemy’s Hypothesis

As referenced before, Ptolemy’s hypothesis can be stretched out to a cyclic pentagon and used to demonstrate the connection of the brilliant proportion between its sides and diagonals.

For an ordinary cyclic pentagon ABCDE, the sides are of length ‘a’ and the diagonals are of length ‘d’.

Zeroing in just on the quadrilateral ABCD and applying Ptolemy’s hypothesis, we get:


subbing the particular length values,

d.d = a.d + a.a

d2 = a.d + a2

Allow the above condition to be a2. partition by

d2/a2 = d/a + 1

Presently let the proportion ‘d/a’ be addressed by ‘r’.

In this way, r2 = r + 1

adjust, r2 – r – 1 = 0

Settling for R,

R = (1 ± 5)/2

R = 1.618033…

Hence, the proportion of the sides of a customary pentagon to its diagonals (r = d/a = 1.618033) is the brilliant proportion.

Likewise, utilizing Ptolemy’s hypothesis to demonstrate the Pythagorean hypothesis

ABCD is a square shape recorded inside a circle.

Applying Ptolemy’s hypothesis to the square shape ABCD, we have


For a given square shape, inverse sides are equivalent, as are two diagonals. In this way, Stomach muscle = Compact disc, AC = BD and Promotion = BC.

BC2 = AB2+ AC2

The above condition is only Pythagoras hypothesis which is relevant to right calculated triangle ABC.

one final word

Notwithstanding the two results referenced above, Ptolemy utilized the hypothesis of cyclic quadrilaterals to deliver his table of harmonies (a geometrical table like the table of upsides of the sine capability that we actually use today). While not the first of its sort, Ptolemy’s harmony table furnished upsides of geometrical capabilities with additions of 30′, while the main geometry table made by Hipparchus gave values at augmentations of 7°30′.

This brought about undeniably more precise projections and determined the places of different planets, the Sun, the Moon, the rising and setting of stars, the dates of lunar and sun based shrouds, and so forth.

The blend of Ptolemy’s galactic work showed up as thirteen books, referred to on the whole as the Almagest, thought about perhaps of the most persuasive work in the field of cosmology. His work outperformed all past cosmic works, ruled for a long time and was subsequently loved as the best galactic work of days of yore.

A considerable lot of Ptolemy’s galactic accomplishments could never have been conceivable without the utilization of the table of harmonies, not so much for Ptolemy’s hypothesis of cyclic quadrilaterals!

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