Tana = 1/ Seka
tan2a=2tana/( 1+tan^2 a)
Trigonometric function is a transcendental function in elementary functions in mathematics. Their essence is the mapping between any set of angles and a set of ratio variables. The usual trigonometric function is defined in a plane rectangular coordinate system. Its definition field is the whole real number field. The other is defined in a right triangle, but it is incomplete. Modern mathematics describes them as the limit of infinite sequence and the solution of differential equation, and extends their definitions to complex system.
Extended data:
1. Let α be an arbitrary angle, and the values of the same trigonometric function with the same terminal angle are equal: tan(2kπ+α)=tanα.
2. Let α be an arbitrary angle, and the relationship between π+α and the trigonometric function value of α is tan(π+α)=tanα.
3. The relationship between arbitrary angle α and trigonometric function value of-α: tan (-α) =-tan α.
4. The relationship between π-α and the trigonometric function value of α can be obtained by Formula 2 and Formula 3: tan (π-α) =-tan α.
5. Using formula 1 and formula 3, we can get the relationship between the trigonometric function values of 2π-α and α: tan (2π-α) =-tan α.