= (n-1)/n * (n-3)/(n-2) * … * 4/5 * 2/3, where n is an odd number;

= (n-1)/n * (n-3)/(n-2) * … * 3/4 *1/2 * π/2, where n is an even number.

Because of the periodicity of trigonometric function, it does not have the inverse function in the sense of single-valued function.

Trigonometric functions have important applications in complex numbers. In RT△ABC, if the acute angle A is determined, then the ratio of the opposite side to the adjacent side of the angle A is determined accordingly.

Extended data:

X represents the independent variable, that is, X represents the size of the angle and Y represents the function value, so we define the trigonometric function y=sin x at any angle, whose domain is all real numbers, and the range of values is [- 1, 1].

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)

Given the length of three sides of a triangle, three internal angles can be found; The third side can be obtained by knowing the two sides and the included angle of the triangle; Given the diagonal of two sides and one side of a triangle, we can find the other angles and the third side.

Reciprocal relations: tanα cotα= 1+0, sin α CSC α = 1, cos α secα =1; +0;

The relationship of quotient: sinα/cosα=tanα=secα/cscα, cos α/sin α = cot α = CSC α/sec α;

And the relationship: sin2α+cos2α= 1, 1+tan2α=sec2α,1+cot2α = csc2α;

Square relation: sin? α+cos？ α= 1。

Baidu encyclopedia-sine function

Baidu encyclopedia-cosine function