Excerpt from Plane and Spherical Trigonometry
This book originated in a desire to give to my private pupils a better idea of the trigonometric functions of obtuse angles than they could obtain from any book with which I was acquainted.
I believe that a student can get a comprehensive and thorough knowledge of trigonometry most quickly and easily, if, at the outset, such definitions are given to the trigonometric functions as will apply to all angles: with this idea for a basis, I have endeavored to prepare an elementary text-book for general use. By beginning with an explanation of the use of the negative sign as applied to lines and angles, and then giving general definitions to the trigonometric functions, I have been able to demonstrate all the fundamental formulas in a perfectly general yet simple manner.
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