Sumerian astronomers studied angle measure, using a division of circles into 360 degrees. They, and later the Babylonians, studied the ratios of the sides of similartriangles and discovered some properties of these

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Trigonometric ratios are the ratios between edges of a right triangle. These ratios are given by the following trigonometric functions of the known angle A, where a, b and c refer to the lengths of the sides in the accompanying figure:
• Sinefunction

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Using the unit circle, one can extend the definitions of trigonometric ratios to all positive and negative arguments (see trigonometric function).
Graphs of trigonometric

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Astronomy
For centuries, spherical trigonometry has been used for locating solar, lunar, and stellar positions, predicting eclipses, and describing the orbits of the planets.
In modern times, the technique of triangulationis

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• Aryabhata's sine table
• Generalized trigonometry
• Lénárt sphere

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• Boyer, Carl B. (1991). A History of Mathematics (Second ed.). John Wiley & Sons, Inc. ISBN 978-0-471-54397-8.
• Nielsen, Kaj L. (1966). Logarithmic and Trigonometric Tables to Five Places (2nd ed.). New York: Barnes & Noble. LCCN 61-9103.

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Trigonometry has been noted for its many identities, that is, equations that are true for all possible inputs.
Identities involving only angles are known as trigonometric identities. Other equations, known as triangle identities, relate both the sides and

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