The special value of trigonometric function generally refers to the special trigonometric function value, which generally refers to the sine and cosine values and tangent values of angles such as 0, 30, 45, 60, 90, 120, 150 and 180. Trigonometric function values of these angles are often used. And using the formulas of trigonometric functions of the sum and difference of two angles, we can get some trigonometric function values of other angles.

As shown in the following figure: Extension: Trigonometric function Trigonometric function is one of the six basic elementary functions, with angle (the most commonly used radian system in mathematics, the same below) as the independent variable, and the coordinate or its ratio of the intersection of the terminal edge of any angle and the unit circle 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. In mathematical analysis, trigonometric function is also defined as the solution of infinite series or specific differential equation, which allows its value to be extended to any real value or even complex value.

Common trigonometric functions are sine function, cosine function and tangent function.