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)