ABSTRACT
Fields that use trigonometry or trigonometric functions include astronomy, especially for locating apparent positions of celestial objects, in which spherical trigonometry is essential, and hence navigation, music theory, acoustics, optics, analysis of financial markets, electronics, probability theory, statistics, biology, medical imaging. There are an enormous number of uses of trigonometry and trigonometric functions. Trigonometric functions also include pharmacy, chemistry, number theory, seismology, meteorology, oceanography, many physical sciences, land surveying and geodesy, architecture, phonetics, economics, electrical engineering, mechanical engineering, civil engineering, computer graphics, cartography, crystallography and game development. It is clear that a good knowledge of trigonometry is essential in many fields of engineering. The chapter describes the theorem of Pythagoras and use it to find the unknown side of a right-angled triangle. It explains sine, cosine, tangent, secant, cosecant and cotangent of an angle in a right-angled triangle.
