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TRIGONOMETRY.

BY

G. A. WENTWORTH, A.M.,

PROFESSOR OF MATHEMATICS IN PHILLIPS EXETER ACADEMY.

BOSTON:

PUBLISHED BY GINN, HEATH, & CO.
1882.

A

HARVARD COLLEGE LIBRARY

GIFT OF

PROF. PAUL H. HANUS
FEB 7 1935

Entered, according to Act of Congress, in the year 1882, by
G. A. WENTWORTH,

in the office of the Librarian of Congress, at Washington.

GINN, HEATH, & Co., PRINTERS:

J. S. CUSHING, SUPT., 16 HAWLEY STREET,
BOSTON.

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PREFACE.

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IN preparing this work the aim has been to furnish just so much

of Trigonometry as is actually taught in our best schools and colleges. Consequently, development of functions in series and all other investigations that are important only for the special student have been omitted. The principles have been unfolded with the utmost brevity consistent with simplicity and clearness, and interesting problems have been selected with a view to awaken a real love for the study. Much time and labor have been spent in devising the simplest proofs for the propositions, and in exhibiting the best methods of arranging the logarithmic work.

The author is under particular obligation for assistance to G. A. Hill, A.M., of Cambridge, Mass., to whom is chiefly due whatever value the Trigonometry possesses.

PHILLIPS EXETER ACADEMY,

September, 1882.

G. A. WENTWORTH.

PLANE TRIGONOMETRY.

CHAPTER I. FUNCTIONS OF ACUTE ANGLES:

Definitions, 1; representation of functions by lines, 7; changes in the functions as the angle changes, 9; functions of complementary angles, 10; relations of the functions of an angle, 11; formulas for finding all the other functions of an angle when one function of the angle is given, 13; functions of 45o, 30°, 60°, 15.

CHAPTER II. THE RIGHT TRIANGLE :

Solution: Case I., when an acute angle and the hypotenuse are given, 16; Case II., when an acute angle and the opposite leg are given, 17; Case III., when an acute angle and the adjacent leg are given, 17; Case IV., when the hypotenuse and a leg are given, 18; Case V., when the two legs are given, 18; general method of solving the right triangle, 19; area of the right triangle, 20; the isosceles triangle, 24; the regular polygon, 26.

CHAPTER III. GONIOMETRY:

Definition of Goniometry, 28; angles of any magnitude, 28; general definitions of the functions of angles, 29; algebraic signs of the functions, 31; functions of a variable angle, 32; functions of angles larger than 360°, 34; formulas for acute angles extended to all angles, 35; reduction of the functions of all angles to the functions of angles in the first quadrant, 38; functions of angles that differ by 90°, 40; functions of a negative angle, 41; functions of the sum of two angles, 43; functions of the difference of two angles, 45; functions of twice an angle, 47; functions of half an angle, 47; sums and differences of functions, 48.

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