Let α be an arbitrary angle and the values of the same trigonometric function with the same terminal angle are equal: sin (2kπ+α) = sinα, cos (2kπ+α) = cosα, tan (2kπ+α) = tanα, and cot (2kπ+α) = cotα.

1 ,( ax)′= ax lna .

2.sin(a+b)=sinacosb+cosasinb or cos(a+b)=cosacosb-sinasinb.

3、sin(3α)=3sinα-4sin^3α=4sinαsin(π/3+α)sin(π/3-α).

Universal unit conversion:

(1)1km =1km =1000m1m =10 decimeter1decimeter =10 cm/kloc.

(2) 1 m2 = 100 square decimeter 1 square decimeter = 100 square centimeter 1 square centimeter = 100 square millimeter.

(3) 1 m3 = 1000 cubic decimeter 1 cubic decimeter = 1000 cubic centimeter 1 cubic centimeter = 1000 cubic millimeter.

(4)1t =1000 kg1kg =1000 mg =1kg = 2 kg.

(5) 1 hectare = 1 ten thousand square meters 1 mu =666.666 square meters.