Rational Trigonometry

Today I discovered a “math related post over at Slashdot”:http://science.slashdot.org/science/05/09/17/1313249.shtml?tid=228&tid=14 that definitely sparked my interest. N.J. Wildberger a professor of mathematics at the University of New South Wales in Sydney Australia recently published a book called “Divine Proportions: Rational Trigonometry to Universal Geometry”:http://web.maths.unsw.edu.au.nyud.net:8090/~norman/book.htm:

bq. This text introduces a new and simplified approach to trigonometry and a major restructuring of Euclidean geometry. It replaces cos, sin, tan and all those other transcendental trig functions with rational functions and elementary arithmetic. It develops a complete theory of planar Euclidean geometry over a general field without any reliance on `axioms’.

The new approach is based on the dual concepts of spread and quadrance rather than distance and angles. The first chapter is available online in “pdf form”:http://web.maths.unsw.edu.au.nyud.net:8090/~norman/papers/Chapter1.pdf and gives a pretty good break down of how the approach builds on those two concepts. Despite the nearly 10 years since my last math class I was able to grasp the material on a basic level pretty quickly and it looks promising. If the book wasn’t “priced like a typcial text book”:http://wildegg.com/order.htm I would seriously consider purchasing it when it becomes available.

I’m really curious to see how the mathematics community around the world will react to these ideas. As Dr. Wildberger puts it in his introduction:

bq. In the Roman period, which saw the beginnings of classical trigonometry, arithmetic used Roman numerals (such as the page numbers in this introduction). Cities were built, students were taught, and an empire was administered, with an arithmetic that was cumbersome and hard to learn, at least when compared to the one we now use built from the Arabic-Hindu numerical
system. Today we understand that the difficulty with arithmetic in Roman times was largely due to the awkward conceptual framework.

bq. Much the same holds, in my opinion, for classical trigonometry–it has been such a hurdle to generations of students not because of the essential intractability of the subject, but rather because the basic notions used to study it for the last two thousand years are not the right ones.

bq. By the time you have finished this book, you should be comfortable with the fact that geometry is a quadratic subject, requiring quadratic mathematics. Using more or less linear ideas, such as distance and angle, may be initially appealing but is ultimately inappropriate. With the natural approach of rational trigonometry, many more people should be able to appreciate the rich patterns of geometry and perhaps even experience the joy of mathematical discovery.

Definitely non traditional stuff, but it looks pretty promising to me and definitely something I want to keep an eye on.

2 comments:

  1. Thomas, 18. February 2006, 12:13

    Rational Trigonometry uses nonlinear units (quadrances and spreads) and is not appropriate for most science and engineering problems that rely on a linear system of measures. For example, a spread is periodic and cannot express a rotation beyond 90 degrees. Similarly, doubling or halving the length of line doesn’t double or halve its quadrance. In general, quadrances and spreads can’t be added or subtracted in the same way that distances, degrees and radian measures can. Wildberger downplays the importance of linearity implying that good (rational) answers are more important than linearity. Most scholars may disagree.

    Wildberger’s brief introduction to history is incomplete. He fails to provide a reason for why the ancient mathematicians and astronomers went to using trigonometric tables. It was because their form of ‘rational trigonometry’ was nonlinear, and they needed a means to transform nonlinear measurements (chords and sines) to a linear unit (degree).

    Wildberger’s comparison of rational trigonometry with classical trigonometry is invalid. He makes classical calculations that are unnecessary, and he fails to choose the best classical formulas to calculate the results. Unlike classical trigonometry, rational trigonometry sometimes requires solving simultaneous linear or quadratic equations or using the quadratic formula.

    As you can see, the subject is quite controversial.

     
  2. Jimmy Roberts, 4. March 2006, 8:08

    A comparison of rational trigonometry and classical trigonometry can be found here:

    http://www.geocities.com/xyz.abc_123/rationalTrig/TrigComparison.pdf

    A discussion on this subject can also be found at the Drexel Univ Math Forum:

    http://mathforum.org/kb/message.jspa?messageID=4110480

     

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