Trigonometry (from Greek trigōnon, “triangle” and metron, “measure” ) is a branch of mathematics that studies relationships between side lengths and angles of triangles. The field emerged in the Hellenistic world during the 3rd century BC from applications of geometry to astronomical studies. The Greeks focused on the calculation of chords, while mathematicians in India created the earliest-known tables of values for trigonometric ratios (also called trigonometric functions) such as sine. Throughout history, trigonometry has been applied in areas such as geodesy, surveying, celestial mechanics, and navigation. Trigonometry is known for its many identities. These trigonometric identities are commonly used for rewriting trigonometrical expressions with the aim to simplify an expression, to find a more useful form of an expression, or to solve an equation. [1]
References
[1] “Trigonometry – Wikipedia”. 2021. en.wikipedia.org. https://en.wikipedia.org/wiki/Trigonometry.
Additional Reading
“Hipparchus – Wikipedia”. 2021. en.wikipedia.org. https://en.wikipedia.org/wiki/Hipparchus.
Hipparchus of Nicaea (/hɪˈpɑːrkəs/; Greek: Ἵππαρχος, Hipparkhos; c. 190 – c. 120 BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry. He developed trigonometry and constructed trigonometric tables, and he solved several problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses.
[ ℰ ] Alshi, Hrishikesh. “The Hidden Geometry Behind Trigonometry: Why Math Class Made No Sense.” Medium, October 5, 2026. https://medium.com/@hrishikeshalshi/the-hidden-geometry-behind-trigonometry-why-math-class-made-no-sense-46f47a1626d1.
Trigonometric terms like Sine, Cosine, and Tangent are not arbitrary labels but precise geometric descriptions. Historically, “Sine” evolved from a Sanskrit term for a bowstring, mistranslated through Arabic into Latin. The prefix “co-” denotes complementary angles, while Tangent and Secant represent lines that “touch” or “cut” a circle. By visualizing these functions as physical segments on a unit circle, trigonometry transforms from abstract memorization into intuitive, historical geometry.
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