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The term "trigonometry" was derived from Greek τρίγωνον trigōnon, "triangle" and μέτρον metron, "measure". [3]The modern words "sine" and "cosine" are derived from the Latin word sinus via mistranslation from Arabic (see Sine and cosine § Etymology).
By restricting the domain of a trigonometric function, however, they can be made invertible. [ 42 ] : 48ff The names of the inverse trigonometric functions, together with their domains and range, can be found in the following table: [ 42 ] : 48ff [ 43 ] : 521ff
Book II deals with "that noble kind of Geometry, that is called Trigonometry." The first chapter deals with using logarithms to solve problems in plane trigonometry with right triangles and, in particular, with small angles, where his trigonometric logarithms become large. The next chapter cover plane oblique triangles.
Nevertheless, in the centuries that followed significant advances were made in applied mathematics, most notably trigonometry, largely to address the needs of astronomers. [74] Hipparchus of Nicaea ( c. 190 –120 BC) is considered the founder of trigonometry for compiling the first known trigonometric table, and to him is also due the ...
In doing so, he discovered a connection between Riemann zeta function and prime numbers, known as the Euler product formula for the Riemann zeta function. Euler proved Newton's identities , Fermat's little theorem , Fermat's theorem on sums of two squares , and made distinct contributions to the Lagrange's four-square theorem .
4th to 5th centuries: The modern fundamental trigonometric functions, sine and cosine, are described in the Siddhantas of India. [75] This formulation of trigonometry is an improvement over the earlier Greek functions, in that it lends itself more seamlessly to polar co-ordinates and the later complex interpretation of the trigonometric functions.
James Gregory FRS (November 1638 – October 1675) was a Scottish mathematician and astronomer.His surname is sometimes spelt as Gregorie, the original Scottish spelling.He described an early practical design for the reflecting telescope – the Gregorian telescope – and made advances in trigonometry, discovering infinite series representations for several trigonometric functions.
For tiny arcs, the chord is to the arc angle in degrees as π is to 3, or more precisely, the ratio can be made as close as desired to π / 3 ≈ 1.047 197 55 by making θ small enough. Thus, for the arc of 1 / 2 ° , the chord length is slightly more than the arc angle in degrees.