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| | Trigonometric function |
 | | In mathematics, the trigonometric functions are functionss of an angle, important when studying triangless and modeling periodic phenomena. |
 | | They may be defined as ratios of two sides of a right triangle containing the angle, or, more generally, as ratios of coordinates of points on the unit circle, or, more generally still, as infinite series, or equally generally, as solutions of certain differential equations. |
 | | A few other functions were common historically (and appeared in the earliest tables), but are now little-used, such as the versed sine (versin = 1 − cos) and the exsecant (exsec = sec − 1). |
| www.sciencedaily.com /encyclopedia/trigonometric_function (2572 words) |
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