1, acute angle formula of trigonometric function: opposite side/hypotenuse of sinα=∞α; Adjacent side/hypotenuse of cosα=∞α; Opposite side of tanα = adjacent side of ∠ α/∠α; Cot α = ∠ α = adjacent side of ∠α/opposite side of ∠α;

2. Double angle formula Sin2A=2SinA? CosAcos2a=cosa^2-sina^2= 1-2sina^2=2cosa^2- 1； tan2a=(2tana)/ 1-tana^2)；