FELIX KLEIN ELEMENTARY MATHEMATICS FROM AN ADVANCED STANDPOINT- ARITHMETIC- ALGEBRA -ANALYSIS. TRANSLATED FROM THE THIRD GERMAN EDlTION BY E. R. HEDRICK AND C, A. NOBLE PROFESSOR OF MATHEMATICS PROFESSOR OF MATHEMATICS IN THE UNIVERSITY OF CALIFORNIA IN THE UNIVERSITY OF CALIFORNIA AT LOS ANGELES AT BERKELEY WITH 125 FIGURES MACMILLAN AND CO., LIMITED ST. MARTINS STREET, LONDON 1932 ALL RIGHTS RESERVED PRINTED IN GERMANY BY THE SPAMERSCHE BUCHDRUCKEREI LEIPZIG Preface to the First Edition. The new volume which I herewith offer to the mathematical public, and especially to the teachers of mathematics in our secondary schools, is to be looked upon as a first continuation of the lectures Uber den mathematischen Unterricht an den hoheren Schulen, in particular, of those on Die Organisation des mathematischen Unterrichts by Schimmack and me, which were published last year by Teubner. At that time our concern was with the different ways in which the problem of instruction can be presented to the mathematician. At present my concern is with deve lopments in the subject matter of instruction. I shall endeavor to put before the teacher, as well as the maturing student, from the view-point of modern science, but in a manner as simple, stimulating, and convincing as possible, both the content and the foundations of the topics of instruction, with due regard for the current methods of teaching. I shall not follow a systematically ordered presentation, as do, for example, Weber and Wellstein, but I shall allow myself free excursions as the changing stimulus of surroundings may lead me to do in the course of the actual lectures. The program thus indicated, which for the present is to be carried out only for the fields of Arithmetic, Algebra, and Analysis, was indicated in the preface to Klein-Schimmack April 1907. I had hoped then that Mr.. Schimmack, in spite of many obstacles, would still find the time to put my lectures into form suitable for printing. But I myself, in a way, prevented his doing this by continuously claiming his time for work in another direction upon pedagogical questions that interested us both. It soon became clear that the original plan could not be carried out, particularly if the work was to be finished in a short time, which seemed desirable if it was to have any real influence upon those problems of instruction which are just now in the foreground, As in previous years, then, I had recourse to the more convenient method of lithographing my lectures, especially since my present assistant, Dr. Ernst Hellinger, showed himself especially well qualified for this work. One should not underestimate the service which Dr. Hellinger rendered. For it is a far cry from the spoken word of the teacher, influenced as it is by accidental conditions, to the subsequently polished and readable record. On the teaching of mathematics in the secondary schools. The organization of mathematical instruction. IV In precision of statement and in uniformity of explanations, the lecturer stops short of what we are accustomed to consider necessary for a printed publication. I hesitate to commit myself to still further publications on the teaching of mathematics, at least for the field of geometry. I prefer to close with the wish that the present lithographed volume may prove useful by inducing many of the teachers of our higher schools to renewed use of independent thought in determining the best way of presenting the material of instruction. This book is designed solely as such a mental spur, not as a detailed handbook. The preparation of the latter I leave to those actively engaged in the schools. It is an error to assume, as some appear to have done, that my activity has ever had any other purpose...