There are six basic functions: function names: sine, cosine, tangent, cotangent, secant and cotangent.
Symbols: sin, cos, tan, cot, sec, csc.
Sine function sin (a) = a/c.
Cosine function cos (a) = b/c.
Tangent function tan (a) = a/b.
Cotangent function cot (a) = b/a.
Where a is the opposite side, b is the adjacent side and c is the hypotenuse.
Brief introduction of trigonometric function
Maurolico used symbols for trigonometric functions as early as 1558, but there was no concept of function at that time, so it was just called river line. He used sine 1m arc and cosine 2m arc.
Trigonometric function is one of the basic elementary functions, which takes the angle (the most commonly used radian system in mathematics, the same below) as the independent variable, and the angle corresponds to the coordinates where the terminal edge of any angle intersects with the unit circle or its ratio as the dependent variable. It can also be equivalently defined as the lengths of various line segments related to the unit circle.
Trigonometric function plays an important role in studying the properties of geometric shapes such as triangles and circles, and is also a basic mathematical tool for studying periodic phenomena.