Trigonometric function is a common function about angle in mathematics. In other words, a function with angle as the independent variable and the ratio of angle to any two sides as the dependent variable is called trigonometric function, which relates the inner angle of a right triangle to the ratio of the lengths of its two sides, and 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 infinite limit or the solution of a specific differential equation, which allows its value to be extended to any real value or even complex value.

Trigonometric function values with special angles are often used, and it is helpful to keep these in mind to improve the speed of solving problems.