AN ELEMENTARY TREATISE ON . TRILINEAR CO-ORDINATES, THE METHOD OF RECIPROCAL POLARS, BY THE REV. N. M. FERRERS, M.A. FELLOW AND TUTOR OF GONVILLE AND CAIUS COLLEGE. HE UNIVERSITY CALIFORNIA THIRD EDITION. London: MACMILLAN AND CO. 1876. [All Rights reserved.] 다 PREFACE. THE prominence which the modern geometrical methods have recently acquired in the studies of the University of Cambridge, appears to justify the publication of a treatise devoted exclusively to these branches of Mathematics. This remark applies more especially to the method of Trilinear Co-ordinates, which forms the subject of the greater part of the following work. My object in writing on this subject has mainly been to place it on a basis altogether independent of the ordinary Cartesian system, instead of regarding it as only a special form of Abridged Notation. A desire not unduly to increase the size of the book has prevented me from proceeding beyond Curves of the Second Degree. In this Second Edition several new articles have been added, especially in the latter part of the work, and the chapter on Reciprocal Polars considerably enlarged. GONVILLE AND CAIUS COLLEGE, N. M. F. In the Third Edition, I have rewritten some articles where the demonstrations were imperfect or obscure, and have added some examples, taken from various Cambridge Examination papers. DECEMBER, 1875. Investigation of Equations of certain Straight Lines Every Straight Line may be represented by an Equation of the Equation of a Straight Line passing through Two given Points. ib. Equation of a Straight Line passing through the Point of Inter- section of Two given Straight Lines Condition that Three Points may lie in the same Straight Line Condition that Three Straight Lines may intersect in a Point . Inclination of a Straight Line to a side of the Triangle of Refer- The Anharmonic Ratio of a Pencil is equal to that of the range in which it is cut by any Transversal Definition of an Harmonic Pencil |