Ancient Greece

220 quotes found

"The theory of proportions is credited to Eudoxus... and is expounded in Book V of Euclid's Elements. The purpose of the theory is to enable lengths (and other geometric quantities) to be treated as precisely as numbers, while only admitting the use of rational numbers. ...To simplify ...let us call lengths rational if they are rational multiples of a fixed length. Eudoxus' idea was to say that a length \lambda is determined by those rational lengths less than it and those greater than it. ...he says \lambda_1 = \lambda_2...if any rational length < \lambda_1 is also < \lambda_2, and vice versa [any rational length > \lambda_2 is also > \lambda_1]. Likewise \lambda_1 < \lambda_2 if there is a rational length > \lambda_1 but < \lambda_2 [between \lambda_1 and \lambda_2]. This definition uses the rationals to give an infinitely sharp notion of length while avoiding any overt use of infinity. ... The theory of proportions was so successful that it delayed the development of a theory of real numbers for 2000 years. This was ironic, because the theory of proportion can be used to define irrational numbers just as well as lengths. It was understandable though, because the common irrational lengths... arise from constructions that are intuitively clear and finite from the geometric point of view. Any arithmetic approach to the \sqrt2, whether by sequences, decimals, or continued fractions, is infinite and therefore less intuitive. Until the nineteenth century this seemed a good reason... Then the problems of geometry came to a head, and mathematicians began to fear geometric intuition as much as they had previously feared infinity."

- Ancient Greek mathematics

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"One of the central concepts for the understanding of ancient Greek mathematics has customarily been, at least since the time of and , the concept of 'geometric algebra'. What it amounts to is that Greek mathematics, especially after the discovery of the 'irrational'... is algebra dressed up, primarily for the sake of rigor, in geometrical garb. The reasoning... the line of attack... the solutions... etc. all are essentially algebraic... attired in geometrical accouterments. We... look for the algebraic 'subtext'... of any geometrical proof... always to transcribe... any proposition in[to] the symbolic language of modern algebra... [making] the logical structure of the proof clear and convincing, without thereby losing anything, not only in generality but also in any possible sui generis features of the ancient way of doing things. ...[i.e., that] there is nothing unique and (ontologically) idiosyncratic concerning the way... ancient Greek mathematicians went about their proofs, which might be lost... I cannot find any historically gratifying basis for this generally accepted view... those who have been writing the history of mathematics... have typically been mathematicians... largely unable to relinquish and discard their laboriously acquired mathematical competence when dealing with periods in history during which such competence is historically irrelevant and... anachronistic. Such... stems from the unstated assumption that mathematics is a scientia universalis, an algebra of thought containing universal ways of inference, everlasting structures, and timeless, ideal patterns of investigation which can be identified throughout the history of civilized man and which are completely independent of the form in which they happen to appear at a particular junction of time."

- Ancient Greek mathematics

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"The Greeks would have said... we know a much better way of taking a square root. ...the ancient Greeks thought entirely geometrically, not arithmetically. And they would... do the following. If you want to solve x^2 = N, you should first... think of whether N is bigger than or equal to one. Suppose that case 1) N < 1. ...Draw a [horizontal] line segment of length one and then [within and from the end of that segment]... make a segment of size N. And then with the center of the [length one] segment you draw a circle so this is a [unit length] diameter. And you... [draw a vertical line from the end of the N segment inside the circle] up here [to intersect the circle] and then... look at this quantity x... this [top angle of the largest triangle circumscribed by the circle] is a right angle by Thales theorem, so we have some similar triangles. So [side x, side 1 from the large circumscribed triangle] \frac{x}{1} = \frac{N}{x} [side N, side x from the small left triangle] by similar \triangle's . And so x^2 = N. So Geometrically finding a square root is... a relatively simple... rule or construction, but arithmetically much more difficult. What happens if N is bigger than one? Well then you just interchange the roles of the N and the one. Case 2) N \ge 1. So you start by having a diameter of size N and then you make [a line segment of length] 1 here [from the end of the segment of length N to within that segment] and then otherwise do exactly the same thing [as in the above, case 1]. ...x will be square root, x^2 = N, by the same argument."

- Ancient Greek mathematics

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"vi. The angle in a semicircle is a right angle. It is believed that Thales proved this proposition in the following manner: Let ABCH be a circle of which the diameter is BC, and the centre E. ...Draw AE and produce BA to F. Because BE is equal to EA [both being radii of the circle], the angle EAB is equal to EBA; also, because AE is equal to EC, the angle EAC is equal to ECA [being angles at the base of an isosceles triangle]; wherefore, the whole angle BAC is equal to the two angles ABC, ACB. But FAC, the exterior angle of the triangle ABC, is also equal to the two angles ABC, ACB [since the sum of the three angles of the triangle is equal to two right angles, i.e., a straight line]; therefore the angle BAC is equal to the angle FAC, and each of them is therefore a right angle; wherefore the angle BAC in a semicircle is a right angle. Thales's demonstration, if we may call this his, is quite different from the one given in modern text-books; but it is certainly neither less rigid nor less beautiful. The demonstration is the one given in Euclid, but his work, we must remember, is to a large extent compiled from the works of previous writers. It will be seen, however, that this demonstration implies a knowledge of a seventh proposition,—"If one side of a triangle be produced, the exterior angle is equal to the sum of the two interior and opposite angles." Thales must have been familiar with this truth."

- Ancient Greek mathematics

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"Two curious nations there have been - sprung of the same race, but placed in different circumstances and environments, working put the problems of life each in its own particular way. I mean the ancient Hindu and the ancient Greek. The Indian Aryan - bounded on the north by the snow-caps of the Himalayas, with fresh-water rivers like rolling oceans surrounding him in the plains, with eternal forests which, to him, seemed to be the end of the world - turned his vision inward; and given the natural instinct, the superfine brain of the Aryan, with this sublime scenery surrounding him, the natural result was that he became introspective. The analysis of his own mind was the great theme of the Indo-Aryan. With the Greek, on the other hand, who arrived at a part of the earth which was more beautiful than sublime, the beautiful islands of the Grecian Archipelago, nature all around him generous yet simple - his mind naturally went outside. It wanted to analyse the external world. And as a result we find that from India have sprung all the analytical sciences, and from Greece all the sciences of generalization. The Hindu mind went on in its own direction and produced the most marvellous results. Even at the present day, the logical capacity of the Hindus, and the tremendous power which the Indian brain still possesses, is beyond compare. ...Today the ancient Greek is meeting the ancient Hindu on the soil of India."

- Ancient Greece–Ancient India relations

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