Isoangular formulas of trigonometric functions is tanαcotα= 1, sinαcscα= 1, cosαsecα= 1, sinα/cosα=tanα, sin 2 (α)+cos 2 (α) = 1, and so on.

Trigonometric function is one of the basic elementary functions, which takes the angle (the most commonly used radian system in mathematics) as the independent variable, and the angle corresponds to the coordinates of the intersection point between the terminal edge of any angle and 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.