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In mature symbolic algebra, from Viete onward, the handling of several algebraic unknowns was routine. Before Luca Pacioli, on the other hand, the simultaneous manipulation of three algebraic unknowns was absent from European algebra and the use of two unknowns so infrequent that it has rarely been observed and never analyzed. The present paper analyzes the five occurrences of two algebraic unknowns in Fibonacci's writings; the gradual unfolding of the idea in Antonio de' Mazzinghi's Fioretti; the distorted use in an anonymous Florentine algebra from ca 1400; the regular appearance in the treatises of Benedetto da Firenze; and finally what little we find in Pacioli's Perugia manuscript and in his Summa. It asks which of these appearances of the technique can be counted as independent rediscoveries of an idea present since long in Sanskrit and Arabic mathematics - metaphorically, to which extent they represent reinvention of the hot water already available on the cooker in the neighbour's kitchen; and it raises the question why the technique once it had been discovered was not cultivated - pointing to the line diagrams used by Fibonacci as a technique that was as efficient as rhetorical algebra handling two unknowns and much less cumbersome, at least until symbolic algebra developed, and as long as the most demanding problems with which algebra was confronted remained the traditional recreational challenges.

The Jainas have always been very interested in mathematics. A renowned 9th century Jaina mathematician monk Mahāvīrācārya authored the famous book Gaṇita-sāra-saṅgraha in 850 CE. Though the work mainly deals with arithmetic, many topics on algebra, geometry and mensuration are also discussed here. In this article an effort is made to discuss about his contributions pertaining to geometry in detail. We shall also highlight some concepts of present-day geometry (including mensuration) that are implicit in this medieval work.

Semi-prime factorization is an increasingly important number theoretic problem, since it is computationally intractable. Further, this property has been applied in public-key cryptography, such as the Rivest–Shamir–Adleman (RSA) encryption systems for secure digital communications. Hence, alternate approaches to solve the semi-prime factorization problem are proposed. Recently, Pythagorean tuples to factor semi-primes have been explored to consider Fermat’s Christmas theorem, with the two squares having opposite parity. This paper is motivated by the property that the integer separating these two squares being odd reduces the search for semi-prime factorization by half. In this paper, we prove that if a Pythagorean quadruple is known and one of its squares represents a Pythagorean triple, then the semi-prime is factorized. The problem of semi-prime factorization is reduced to the problem of finding only one such sum of three squares to factorize a semi-prime. We modify the Lebesgue identity as the sum of four squares to obtain four sums of three squares. These are then expressed as four Pythagorean quadruples. The Brahmagupta–Fibonacci identity reduces these four Pythagorean quadruples to two Pythagorean triples. The greatest common divisors of the sides contained therein are the factors of the semi-prime. We then prove that to factor a semi-prime, it is sufficient that only one of these Pythagorean quadruples be known. We provide the algorithm of our proposed semi-prime factorization method, highlighting its complexity and comparative advantage of the solution space with Fermat’s method. Our algorithm has the advantage when the factors of a semi-prime are congruent to 1 modulus 4. Illustrations of our method for real-world applications, such as factorization of the 768-bit number RSA-768, are established. Further, the computational viabilities, despite the mathematical constraints and the unexplored properties, are suggested as opportunities for future research.

A Brahmagupta quadrilateral is a cyclic quadrilateral whose sides, diagonals and area are all integer values. In this article, we characterise the notions of Brahmagupta, introduced by K. R. S. Sastry [‘Brahmagupta quadrilaterals’, Forum Geom. 2 (2002), 167–173], by means of elliptic curves. Motivated by these characterisations, we use Brahmagupta quadrilaterals to construct infinite families of elliptic curves with torsion group $\\def \\xmlpi #1{}\\def \\mathsfbi #1{\\boldsymbol {\\mathsf {#1}}}\\let \\le =\\leqslant \\let \\leq =\\leqslant \\let \\ge =\\geqslant \\let \\geq =\\geqslant \\def \\Pr {\\mathit {Pr}}\\def \\Fr {\\mathit {Fr}}\\def \\Rey {\\mathit {Re}}\\mathbb{Z}/2\\mathbb{Z}\\times \\mathbb{Z}/2\\mathbb{Z}$ having ranks (at least) four, five and six. Furthermore, by specialising we give examples from these families of specific curves with rank nine.

We continue our analysis of Brahmagupta's Brāhmasphutasiddhānta (India, 628), that had shown that each of his sequences of propositions should be read as an apodictic discourse: a connected discourse that develops the natural consequences of explicitly stated assumptions, within a particular conceptual framework. As a consequence, we established that Brahmagupta did provide a derivation of his results on the cyclic quadrilateral. We analyze here, on the basis of the same principles, further problematic passages in Brahmagupta's magnum opus, regarding number theory and algebra. They make no sense as sets of rules. They become clear as soon as one reads them as an apodictic discourse, so carefully composed that they leave little room for interpretation. In particular, we show that (i) Brahmagupta indicated the principle of the derivation of the solution of linear congruences (the kuttaka) at the end of chapter 12 and (ii) his algebra in several variables is the result of the extension of operations on numbers to new types of quantities - negative numbers, surds and \"non-manifest\" variables.

Based on extensive research in Sanskrit sources, Mathematics in India chronicles the development of mathematical techniques and texts in South Asia from antiquity to the early modern period. Kim Plofker reexamines the few facts about Indian mathematics that have become common knowledge--such as the Indian origin of Arabic numerals--and she sets them in a larger textual and cultural framework. The book details aspects of the subject that have been largely passed over in the past, including the relationships between Indian mathematics and astronomy, and their cross-fertilizations with Islamic scientific traditions. Plofker shows that Indian mathematics appears not as a disconnected set of discoveries, but as a lively, diverse, yet strongly unified discipline, intimately linked to other Indian forms of learning.

In the seventh century, around 650 A.D., the Indian mathematician Brahmagupta came up with a remarkable formula expressing the area E of a cyclic quadrilateral in terms of the lengths a, b, c, d of its sides. In his formula E = [square root](s-a)(s-b)(s-c)(s-d), s stands for the semiperimeter 1/2(a+b+c+d). The fact that Brahmagupta's formula is symmetric in a, b, c, d suggests that there are different cyclic quadrilaterals having the same area and the same side lengths, though the sides may be in different orders. Since the vertices of a cyclic quadrilateral lie on a circle, then actually there are only three orders for the sides, namely (a, b, c, d), (a, b, d, c), and (a, c, b, d), where a is opposite to c, d and b respectively. The author will show that the three quadrilaterals, corresponding to these orders, can be inscribed in the same circle. He will calculate the lengths of their diagonals and the radius of their circumcircle. Before he does that, he will furnish a proof for Brahmagupta's formula. He applies basic geometric and trigonometric results which would make the content of this article usable in the classroom. (Contains 3 figures.)

The Greek astronomer Ptolemy of Alexandria (second century) and the Indian mathematician Brahmagupta (sixth century) each have a significant theorem named after them. Both theorems have to do with cyclic quadrilaterals. Ptolemy's theorem states that: In a cyclic quadrilateral, the product of the diagonals is equal to the sum of the products of two pairs of opposite sides. If the lengths of the sides of a cyclic quadrilateral are a, b, c, d in this order and the lengths of the diagonals are l and k, then Ptolemy's theorem would be expressed as lk = ac + bd. On the other hand, Brahmagupta came up with a remarkable formula for the area E of the cyclic quadrilateral, that is E = [square root](s-a)(s-b)(s-c)(s-d), where s stands for the semiperimeter 1/2(a+b+c+d). Around the middle of the 19th century, there appeared generalizations for both theorems that apply to any convex quadrilateral. The German mathematicians C. A. Bretschneider and F. Strehlke each published their own proofs of the generalizations. Since then, more proofs have shown up in the literature. This paper presents new proofs, which could be used in the classroom or as projects outside the classroom. In addition, it looks into some implications of the two generalizations, and shows that they are not independent of each other. (Contains 1 figure.)

Beauregard and Suryanarayan explain how Brahmagupta triangles can be determined. Brahmagupta analyzed the class of heronian triangles having consecutive integer sides.