DOCSLIB.ORG

Equivalents to the Euclidean Parallel Postulate in This Section We Work

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Equivalents to the Euclidean Parallel Postulate in This Section We Work Equivalents to the Euclidean Parallel Postulate In this section we work within neutral geometry to prove that a number of different statements are equivalent to the Euclidean Parallel Postulate (EPP). This has historical importance. We noted before that Euclid’s Fifth Postulate was quite different in tone and complexity from his first four postulates, and that Euclid himself put off using the fifth postulate for as long as possible in his development of geometry. The history of mathematics is rife with efforts to either prove the fifth postulate from the first four, or to find a simpler postulate from which the fifth postulate could be proved. These efforts gave rise to a number of candidates that, in the end, proved to be no simpler than the fifth postulate and in fact turned out to be logically equivalent, at least in the context of neutral geometry. Euclid’s fifth postulate indeed captured something fundamental about geometry. We begin with the converse of the Alternate Interior Angles Theorem, as follows: If two parallel lines n and m are cut by a transversal l , then alternate interior angles are congruent. We noted earlier that this statement was equivalent to the Euclidean Parallel Postulate. We now prove that. Theorem: The converse of the Alternate Interior Angles Theorem is equivalent to the Euclidean Parallel Postulate. ~ We first assume the converse of the Alternate Interior Angles Theorem and prove that through a given line l and a point P not on the line, there is exactly one line through P parallel to l. We have already proved that one such line must exist: Drop a perpendicular from P to l; call the foot of that perpendicular Q. Let . Now, through point P use the protractor postulate to construct a line m perpendicular to t. The Alternate Interior Angles Theorem guarantees that since the alternate interior angles are all right angles, l and m are parallel. So it all comes down to proving that there is only one such line. To this end, suppose there were another line mN through P parallel to l. By the converse to the Alternate Interior Angles Theorem, alternate interior angles formed by l, mN, and t must be equal, and since t z l we must have mN z t as well. But then m and mN would both be perpendiculars to t though point P, which would violate the uniqueness of rays forming a right angle with t through a given point (Protractor Postulate). Thus, m = mN. To prove the converse, assume that the EPP holds and that l and m are parallel lines cut by a transversal t at points Q and P, respectively. We prove that alternate interior angles are congruent. Suppose for contradiction that alternate interior angles p1 (at point P) and p2 (at point Q) are not congruent, and WLOG that :(p1) > :(p2). Using the protractor postulate, create ray on the other side of t from p2 such that :(pRPQ) = :(p2). Then from the above theorem, since pRPQ and p2 are alternate interior angles, it follows that lines l and are parallel. But that means there are two lines through P parallel to line l, contradicting the parallel postulate. So p1 and p2 are congruent. Theorem: Euclid’s Postulate V is equivalent to the Euclidean Parallel Postulate. ~ First we assume EPP and prove from it Postulate V. Suppose l and m are two lines cut by a transversal t at points P and Q respectively in such a way that the interior angles on one side of t have measures adding to less than 180. Using the Protractor Postulate, construct through point P a line n such that the interior angles formed by n and m (on the same side of t as before) add up to 180. Now a Corollary to the Alternate Interior Angles Theorem, states that if two lines are cut by a transversal such that the interior angles on one side of the transversal are supplementary, the lines are parallel. Thus n and m are parallel, and by EPP n is the only line through P that is parallel to m. Thus l is not parallel to m, and must meet. They must meet on the side of t we have been working on or the triangle they form would have angle measure greater than 180. To prove the converse, let l’ be a line and P a point not on the line. We have demonstrated how we can create a line through P parallel to l’ by using perpendiculars, so we will let l be such a line, created by dropping a perpendicular from P to l’ with foot Q, then forming line l perpendicular to at point P. We now prove there can be no other lines through P parallel to l’. Suppose m is such a line. We know that m cannot be perpendicular to at P since l is, and so the angle it makes with t must have measure less than 90 on one side of t. On that side, the sum of the interior angles formed by m and l’ add to less than 180, and so l’ and m must meet on that side. Thus l’ and m cannot be parallel. Theorem: The following statements are each equivalent to the Euclidean Parallel Postulate (EPP): 1. If l and l’ are parallel lines and is a line such that t intersects l, then t also intersects l’. 2. If l and l’ are parallel lines and t is a transversal such that , then . 3. If l, m, n, and k are lines such that , then either m = n or . 4. If l is parallel to m and m is parallel to n then either l = n or . ~ To prove statement 1 from EPP, let l and l’ be parallel lines and be a line such that t intersects l at point P. By EPP, there can only be one line through point P that is parallel to l’, so t must intersect l’. To prove the converse, let l’ be a line and P a point not on l’. We have demonstrated how we can create a line through P parallel to l’ by using perpendiculars, so we will let l be such a line. We now prove there can be no other lines through P parallel to l’. Let be a line through point P. By statement 1, since t intersects l, it must also intersect l’, and so cannot be parallel to l’. Thus there can only be one line through P which is parallel to l’. To prove statement 2 from EPP, let l and l’ be parallel lines and t a transversal such that . The EPP is equivalent to the converse of the Alternate Interior Angle Theorem, so since l and l’ are parallel, alternate interior angles p1 and p2 must be congruent, and since p1 is a right angle, p2 must be a right angle, so that . To prove the converse, let l’ be a line and P a point not on l’. We have demonstrated how we can create a line through P parallel to l’ by using perpendiculars, so we will let l be such a line, created by dropping a perpendicular from P to l’ with foot Q, then forming line l perpendicular to at point P. We now prove there can be no other lines through P parallel to l’. Suppose m is a line through P parallel to l’. Now is a transversal for m and l’ that is perpendicular to l’ at Q, and so by statement 2 it must also be perpendicular to m at P. But this makes l and m both perpendiculars to at P, contradicting the Protractor Postulate. Thus there cannot be a second parallel m. To prove statement 3 from EPP, we note that we have already proved that statements 1 and 2 above are equivalent to EPP, so we can use them. So let l, m, n, and k be lines such that , and suppose that . In particular, since l and k are parallel and m intersects k, it must also intersect l by statement 1. Moreover, by statement 2, since as well. But then, since and , if we view l as a transversal for m and n we have alternate interior angles congruent, and so . To prove the converse, let l’ be a line and P a point not on l’. We have demonstrated how we can create a line through P parallel to l’ by using perpendiculars, so we will let l be such a line, created by dropping a perpendicular from P to l’ with foot Q, then forming line l perpendicular to at point P. We now prove there can be no other lines through P parallel to l’. Suppose m is a line through P parallel to l’. Drop a perpendicular from Q to m with foot F. Now and , so by statement 3 either , or . Since and clearly share point Q, we must have . Now since can only intersect m once, F = P. But this contradicts the Protractor Postulate, since l and m are both perpendicular to at P. To prove statement 4 from EPP, suppose that l is parallel to m and m is parallel to n , and that l and n are not equal. We prove . Suppose for contradiction that l and n intersect. Then since l is parallel to m, by statement 1, n and m intersect, a contradiction. Thus l and n cannot intersect and are therefore parallel. To prove the converse, let l’ be a line and P a point not on l’.
Load more

Recommended publications
  • Geometry Notes G.2 Parallel Lines, Transversals, Angles Mrs. Grieser Name: Date
    Geometry Notes G.2 Parallel Lines, Transversals, Angles Mrs. Grieser Name: ________________________________________ Date: ______________ Block: ________ Identifying Pairs of Lines and Angles Lines that intersect are coplanar Lines that do not intersect o are parallel (coplanar) OR o are skew (not coplanar) In the figure, name: o intersecting lines:___________ o parallel lines:_______________ o skew lines:________________ o parallel planes:_____________ Example: Think of each segment in the figure as part of a line. Find: Line(s) parallel to CD and containing point A _________ Line(s) skew to and containing point A _________ Line(s) perpendicular to and containing point A _________ Plane(s) parallel to plane EFG and containing point A _________ Parallel and Perpendicular Lines If two lines are in the same plane, then they are either parallel or intersect a point. There exist how many lines through a point not on a line? __________ Only __________ of them is parallel to the line. Parallel Postulate If there is a line and a point not on a line, then there is exactly one line through the point parallel to the given line. Perpendicular Postulate If there is a line and a point not on a line, then there is exactly one line through the point parallel to the given line. Angles and Transversals Interior angles are on the INSIDE of the two lines Exterior angles are on the OUTSIDE of the two lines Alternate angles are on EITHER SIDE of the transversal Consecutive angles are on the SAME SIDE of the transversal Corresponding angles are in the same position on each of the two lines Alternate interior angles lie on either side of the transversal inside the two lines Alternate exterior angles lie on either side of the transversal outside the two lines Consecutive interior angles lie on the same side of the transversal inside the two lines (same side interior) Geometry Notes G.2 Parallel Lines, Transversals, Angles Mrs.
    [Show full text]
  • Proofs with Perpendicular Lines
    3.4 Proofs with Perpendicular Lines EEssentialssential QQuestionuestion What conjectures can you make about perpendicular lines? Writing Conjectures Work with a partner. Fold a piece of paper D in half twice. Label points on the two creases, as shown. a. Write a conjecture about AB— and CD — . Justify your conjecture. b. Write a conjecture about AO— and OB — . AOB Justify your conjecture. C Exploring a Segment Bisector Work with a partner. Fold and crease a piece A of paper, as shown. Label the ends of the crease as A and B. a. Fold the paper again so that point A coincides with point B. Crease the paper on that fold. b. Unfold the paper and examine the four angles formed by the two creases. What can you conclude about the four angles? B Writing a Conjecture CONSTRUCTING Work with a partner. VIABLE a. Draw AB — , as shown. A ARGUMENTS b. Draw an arc with center A on each To be prof cient in math, side of AB — . Using the same compass you need to make setting, draw an arc with center B conjectures and build a on each side of AB— . Label the C O D logical progression of intersections of the arcs C and D. statements to explore the c. Draw CD — . Label its intersection truth of your conjectures. — with AB as O. Write a conjecture B about the resulting diagram. Justify your conjecture. CCommunicateommunicate YourYour AnswerAnswer 4. What conjectures can you make about perpendicular lines? 5. In Exploration 3, f nd AO and OB when AB = 4 units.
    [Show full text]
  • Parallel Lines and Transversals
    5.5 Parallel Lines and Transversals How can you use STATES properties of parallel lines to solve real-life problems? STANDARDS MA.8.G.2.2 1 ACTIVITY: A Property of Parallel Lines Work with a partner. ● Talk about what it means for two lines 12 1 cm 56789 to be parallel. Decide on a strategy for 1234 drawing two parallel lines. 01 91 8 9 9 9 9 10 11 12 13 10 10 10 10 ● Use your strategy to carefully draw 7 67 two lines that are parallel. 14 15 5 16 17 18 19 20 3421 22 23 2 24 25 26 1 ● Now, draw a third line 27 28 in. parallel that intersects the two 29 30 lines parallel lines. This line is called a transversal. 2 1 3 4 6 ● The two parallel lines and 5 7 8 the transversal form eight angles. Which of these angles have equal measures? transversal Explain your reasoning. 2 ACTIVITY: Creating Parallel Lines Work with a partner. a. If you were building the house in the photograph, how could you make sure that the studs are parallel to each other? b. Identify sets of parallel lines and transversals in the Studs photograph. 212 Chapter 5 Angles and Similarity 3 ACTIVITY: Indirect Measurement Work with a partner. F a. Use the fact that two rays from the Sun are parallel to explain why △ABC and △DEF are similar. b. Explain how to use similar triangles to fi nd the height of the fl agpole. x ft Sun’s ray C Sun’s ray 5 ft AB3 ft DE36 ft 4.
    [Show full text]
  • Triangles and Transversals Triangles
    Triangles and Transversals Triangles A three-sided polygon. Symbol → ▵ You name it ▵ ABC. Total Angle Sum of a Triangle The interior angles of a triangle add up to 180 degrees. Symbol = Acute Triangle A triangle that contains only angles that are less than 90 degrees. Obtuse Triangle A triangle with one angle greater than 90 degrees (an obtuse angle). Right Triangle A triangle with one right angle (90 degrees). Vertex The common endpoint of two or more rays or line segments. Complementary Angles Two angles whose measures have a sum of 90 degrees. Supplementary Angles Two angles whose measures have a sum of 180 degrees. Perpendicular Lines Lines that intersect to form a right angle (90 degrees). Symbol = Parallel Lines Lines that never intersect. Arrows are used to indicate lines are parallel. Symbol = || Transversal Lines A line that cuts across two or more (usually parallel) lines. Intersect The point where two lines meet or cross. Vertical Angles Angles opposite one another at the intersection of two lines. Vertical angles have the same angle measurements. Interior Angles An angle inside a shape. Exterior Angles Angles outside of a shape. Alternate Interior Angles The pairs of angles on opposite sides of the transversal but inside the two lines. Alternate Exterior Angles Each pair of these angles are outside the lines, and on opposite sides of the transversal. Corresponding Angles The angles in matching corners. Reflexive Angles An angle whose measure is greater than 180 degrees and less that 360 degrees. Straight Angles An angle that measures exactly 180 degrees. Adjacent Angles Angles with common side and common vertex without overlapping.
    [Show full text]
  • Understand the Principles and Properties of Axiomatic (Synthetic
    Michael Bonomi Understand the principles and properties of axiomatic (synthetic) geometries (0016) Euclidean Geometry: To understand this part of the CST I decided to start off with the geometry we know the most and that is Euclidean: − Euclidean geometry is a geometry that is based on axioms and postulates − Axioms are accepted assumptions without proofs − In Euclidean geometry there are 5 axioms which the rest of geometry is based on − Everybody had no problems with them except for the 5 axiom the parallel postulate − This axiom was that there is only one unique line through a point that is parallel to another line − Most of the geometry can be proven without the parallel postulate − If you do not assume this postulate, then you can only prove that the angle measurements of right triangle are ≤ 180° Hyperbolic Geometry: − We will look at the Poincare model − This model consists of points on the interior of a circle with a radius of one − The lines consist of arcs and intersect our circle at 90° − Angles are defined by angles between the tangent lines drawn between the curves at the point of intersection − If two lines do not intersect within the circle, then they are parallel − Two points on a line in hyperbolic geometry is a line segment − The angle measure of a triangle in hyperbolic geometry < 180° Projective Geometry: − This is the geometry that deals with projecting images from one plane to another this can be like projecting a shadow − This picture shows the basics of Projective geometry − The geometry does not preserve length
    [Show full text]
  • Parallel Lines Cut by a Transversal
    Parallel Lines Cut by a Transversal I. UNIT OVERVIEW & PURPOSE: The goal of this unit is for students to understand the angle theorems related to parallel lines. This is important not only for the mathematics course, but also in connection to the real world as parallel lines are used in designing buildings, airport runways, roads, railroad tracks, bridges, and so much more. Students will work cooperatively in groups to apply the angle theorems to prove lines parallel, to practice geometric proof and discover the connections to other topics including relationships with triangles and geometric constructions. II. UNIT AUTHOR: Darlene Walstrum Patrick Henry High School Roanoke City Public Schools III. COURSE: Mathematical Modeling: Capstone Course IV. CONTENT STRAND: Geometry V. OBJECTIVES: 1. Using prior knowledge of the properties of parallel lines, students will identify and use angles formed by two parallel lines and a transversal. These will include alternate interior angles, alternate exterior angles, vertical angles, corresponding angles, same side interior angles, same side exterior angles, and linear pairs. 2. Using the properties of these angles, students will determine whether two lines are parallel. 3. Students will verify parallelism using both algebraic and coordinate methods. 4. Students will practice geometric proof. 5. Students will use constructions to model knowledge of parallel lines cut by a transversal. These will include the following constructions: parallel lines, perpendicular bisector, and equilateral triangle. 6. Students will work cooperatively in groups of 2 or 3. VI. MATHEMATICS PERFORMANCE EXPECTATION(s): MPE.32 The student will use the relationships between angles formed by two lines cut by a transversal to a) determine whether two lines are parallel; b) verify the parallelism, using algebraic and coordinate methods as well as deductive proofs; and c) solve real-world problems involving angles formed when parallel lines are cut by a transversal.
    [Show full text]
  • Geometry: Neutral MATH 3120, Spring 2016 Many Theorems of Geometry Are True Regardless of Which Parallel Postulate Is Used
    Geometry: Neutral MATH 3120, Spring 2016 Many theorems of geometry are true regardless of which parallel postulate is used. A neutral geom- etry is one in which no parallel postulate exists, and the theorems of a netural geometry are true for Euclidean and (most) non-Euclidean geomteries. Spherical geometry is a special case of Non-Euclidean geometries where the great circles on the sphere are lines. This leads to spherical trigonometry where triangles have angle measure sums greater than 180◦. While this is a non-Euclidean geometry, spherical geometry develops along a separate path where the axioms and theorems of neutral geometry do not typically apply. The axioms and theorems of netural geometry apply to Euclidean and hyperbolic geometries. The theorems below can be proven using the SMSG axioms 1 through 15. In the SMSG axiom list, Axiom 16 is the Euclidean parallel postulate. A neutral geometry assumes only the first 15 axioms of the SMSG set. Notes on notation: The SMSG axioms refer to the length or measure of line segments and the measure of angles. Thus, we will use the notation AB to describe a line segment and AB to denote its length −−! −! or measure. We refer to the angle formed by AB and AC as \BAC (with vertex A) and denote its measure as m\BAC. 1 Lines and Angles Definitions: Congruence • Segments and Angles. Two segments (or angles) are congruent if and only if their measures are equal. • Polygons. Two polygons are congruent if and only if there exists a one-to-one correspondence between their vertices such that all their corresponding sides (line sgements) and all their corre- sponding angles are congruent.
    [Show full text]
  • Thales of Miletus Sources and Interpretations Miletli Thales Kaynaklar Ve Yorumlar
    Thales of Miletus Sources and Interpretations Miletli Thales Kaynaklar ve Yorumlar David Pierce October , Matematics Department Mimar Sinan Fine Arts University Istanbul http://mat.msgsu.edu.tr/~dpierce/ Preface Here are notes of what I have been able to find or figure out about Thales of Miletus. They may be useful for anybody interested in Thales. They are not an essay, though they may lead to one. I focus mainly on the ancient sources that we have, and on the mathematics of Thales. I began this work in preparation to give one of several - minute talks at the Thales Meeting (Thales Buluşması) at the ruins of Miletus, now Milet, September , . The talks were in Turkish; the audience were from the general popu- lation. I chose for my title “Thales as the originator of the concept of proof” (Kanıt kavramının öncüsü olarak Thales). An English draft is in an appendix. The Thales Meeting was arranged by the Tourism Research Society (Turizm Araştırmaları Derneği, TURAD) and the office of the mayor of Didim. Part of Aydın province, the district of Didim encompasses the ancient cities of Priene and Miletus, along with the temple of Didyma. The temple was linked to Miletus, and Herodotus refers to it under the name of the family of priests, the Branchidae. I first visited Priene, Didyma, and Miletus in , when teaching at the Nesin Mathematics Village in Şirince, Selçuk, İzmir. The district of Selçuk contains also the ruins of Eph- esus, home town of Heraclitus. In , I drafted my Miletus talk in the Math Village. Since then, I have edited and added to these notes.
    [Show full text]
  • Neutral Geometry
    Neutral geometry And then we add Euclid’s parallel postulate Saccheri’s dilemma Options are: Summit angles are right Wants Summit angles are obtuse Was able to rule out, and we’ll see how Summit angles are acute The hypothesis of the acute angle is absolutely false, because it is repugnant to the nature of the straight line! Rule out obtuse angles: If we knew that a quadrilateral can’t have the sum of interior angles bigger than 360, we’d be fine. We’d know that if we knew that a triangle can’t have the sum of interior angles bigger than 180. Hold on! Isn’t the sum of the interior angles of a triangle EXACTLY180? Theorem: Angle sum of any triangle is less than or equal to 180º Suppose there is a triangle with angle sum greater than 180º, say anglfle sum of ABC i s 180º + p, w here p> 0. Goal: Construct a triangle that has the same angle sum, but one of its angles is smaller than p. Why is that enough? We would have that the remaining two angles add up to more than 180º: can that happen? Show that any two angles in a triangle add up to less than 180º. What do we know if we don’t have Para lle l Pos tul at e??? Alternate Interior Angle Theorem: If two lines cut by a transversal have a pair of congruent alternate interior angles, then the two lines are parallel. Converse of AIA Converse of AIA theorem: If two lines are parallel then the aliilblternate interior angles cut by a transversa l are congruent.
    [Show full text]
  • Geometry by Its History
    Undergraduate Texts in Mathematics Geometry by Its History Bearbeitet von Alexander Ostermann, Gerhard Wanner 1. Auflage 2012. Buch. xii, 440 S. Hardcover ISBN 978 3 642 29162 3 Format (B x L): 15,5 x 23,5 cm Gewicht: 836 g Weitere Fachgebiete > Mathematik > Geometrie > Elementare Geometrie: Allgemeines Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, eBooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte. 2 The Elements of Euclid “At age eleven, I began Euclid, with my brother as my tutor. This was one of the greatest events of my life, as dazzling as first love. I had not imagined that there was anything as delicious in the world.” (B. Russell, quoted from K. Hoechsmann, Editorial, π in the Sky, Issue 9, Dec. 2005. A few paragraphs later K. H. added: An innocent look at a page of contemporary the- orems is no doubt less likely to evoke feelings of “first love”.) “At the age of 16, Abel’s genius suddenly became apparent. Mr. Holmbo¨e, then professor in his school, gave him private lessons. Having quickly absorbed the Elements, he went through the In- troductio and the Institutiones calculi differentialis and integralis of Euler. From here on, he progressed alone.” (Obituary for Abel by Crelle, J. Reine Angew. Math. 4 (1829) p. 402; transl. from the French) “The year 1868 must be characterised as [Sophus Lie’s] break- through year.
    [Show full text]
  • Euclid Transcript
    Euclid Transcript Date: Wednesday, 16 January 2002 - 12:00AM Location: Barnard's Inn Hall Euclid Professor Robin Wilson In this sequence of lectures I want to look at three great mathematicians that may or may not be familiar to you. We all know the story of Isaac Newton and the apple, but why was it so important? What was his major work (the Principia Mathematica) about, what difficulties did it raise, and how were they resolved? Was Newton really the first to discover the calculus, and what else did he do? That is next time a fortnight today and in the third lecture I will be talking about Leonhard Euler, the most prolific mathematician of all time. Well-known to mathematicians, yet largely unknown to anyone else even though he is the mathematical equivalent of the Enlightenment composer Haydn. Today, in the immortal words of Casablanca, here's looking at Euclid author of the Elements, the best-selling mathematics book of all time, having been used for more than 2000 years indeed, it is quite possibly the most printed book ever, apart than the Bible. Who was Euclid, and why did his writings have such influence? What does the Elements contain, and why did one feature of it cause so much difficulty over the years? Much has been written about the Elements. As the philosopher Immanuel Kant observed: There is no book in metaphysics such as we have in mathematics. If you want to know what mathematics is, just look at Euclid's Elements. The Victorian mathematician Augustus De Morgan, of whom I told you last October, said: The thirteen books of Euclid must have been a tremendous advance, probably even greater than that contained in the Principia of Newton.
    [Show full text]
  • NATHAN SIDOLI and TAKANORI KUSUBA, Nasir Al-Din Al-Tusi's
    Naṣīr al-Dīn al-Ṭūsī’s revision of Theodosius’s Spherics Nathan Sidoli and Takanori Kusuba Keywords: Spherical geometry, spherical astronomy, Spherics, Theodosius, Naṣīr al-Dīn al-Ṭūsī, Greek to Arabic translation, medieval manuscript trans- mission, editorial practices. Abstract We examine the Arabic edition of Theodosius’s Spherics composed by Naṣīr al-Dīn al-Ṭūsī. Through a comparison of this text with earlier Arabic and Greek versions and a study of his editorial remarks, we develop a better un- derstanding of al-Ṭūsī editorial project. We show that al-Ṭūsī’s goal was to revitalize the text of Theodosius’s Spherics by considering it firstly as a prod- uct of the mathematical sciences and secondarily as a historically contingent work. His editorial practices involved adding a number of additional hy- potheses and auxiliary lemmas to demonstrate theorems used in the Spherics, reworking some propositions to clarify the underlying mathematical argu- ment and reorganizing the proof structure in a few propositions. For al-Ṭūsı, the detailed preservation of the words and drawings was less important than a mathematically coherent presentation of the arguments and diagrams. Introduction If the number of the manuscripts may be taken as any indication, during the medieval period, some of the most popular versions of ancient Greek mathe- matical texts were those made in the middle of the 13th century by Abū JaÒfar Suhayl 8 (2008) pp. 9–46 10 Nathan Sidoli and Takanori Kusuba Muḥammad ibn Muḥammad ibn al-Ḥasan Naṣīr al-Dīn al-Ṭūsī. During the course of a long scholarly career, al-Ṭūsī made new Arabic editions of the texts that were then the classics of the mathematical sciences.
    [Show full text]