Sin: British pronunciation: [s? N], American pronunciation: [s? Cos: British pronunciation: [k? z； k？ Z], American pronunciation: [k? Z]. Tan: British pronunciation: [t? N], American pronunciation: [t? n].？

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. This ratio is called the tangent of angle A, and is written as tanA, that is, tanA= the opposite side of angle A/the adjacent side of angle A. ..

In RT△ABC, if the acute angle A is determined, then the ratio of the opposite side to the hypotenuse of the angle A is determined accordingly. This ratio is called sine of angle A, and is recorded as sinA, that is, sinA= the opposite side of angle A/the hypotenuse of angle A. ..

In RT△ABC, if the acute angle A is determined, then the ratio of the adjacent side to the hypotenuse of the angle A is determined. This ratio is called cosine of angle A, and it is recorded as cosA, that is, cosA= adjacent side of angle A/hypotenuse of angle A. ..

Sum angle formula:

1、sin ( α β ) = sinα cosβ cosα sinβ

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

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

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