sin2α=2sinαcosα

tan2α=2tanα/( 1-tan^2(α))

cos2α=cos^2(α)-sin^2(α)=2cos^2(α)- 1= 1-2sin^2(α)？

Half-angle formula of trigonometric function:

sin^2(α/2)=( 1-cosα)/2

cos^2(α/2)=( 1+cosα)/2

tan^2(α/2)=( 1-cosα)/( 1+cosα)

tan(α/2)= sinα/( 1+cosα)=( 1-cosα)/sinα

Double-angle transformation relation of trigonometric function

Double angle formula is to express the trigonometric function value of double angle 2α through some transformation relations of trigonometric function value of angle α. The angle doubling formula includes sine angle doubling formula, cosine angle doubling formula and tangent angle doubling formula.

It can be used to simplify the calculation formula and reduce the number of trigonometric functions in calculation, and it is also widely used in engineering.