sin(2kπ+α)=sinα(k∈Z)

cos(2kπ+α)=cosα(k∈Z)

tan(2kπ+α)=tanα(k∈Z)

cot(2kπ+α)=cotα(k∈Z)

The meaning of the inductive formula formula "even if it changes strangely, the symbol will look at the quadrant";

Trigonometric function value of k× π/2 A (k ∈ z):

(1) When k is an even number, it is equal to the trigonometric function value of the same name of α, preceded by a sign of the original trigonometric function value when α is regarded as an acute angle.

(2) When k is an odd number, different trigonometric function values equal to α are preceded by a sign of the original trigonometric function value when α is regarded as an acute angle.

Sum angle formula:

sin ( α β ) = sinα cosβ cosα sinβ

sin(α+β+γ)= sinαcosβcosγ+cosαsinβcosγ+cosαcosβsinγ-sinαsinβsinγ

cos ( α β ) = cosα cosβ？ Octagonal β-Octagonal α

tan ( α β ) = ( tanα tanβ ) / ( 1？ tanα tanβ)