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)