Quotient relation of trigonometric function: tan α = sin α/cos α; cotα=cosα/sinα.
Square relation: sin? α+cos? α= 1;
1+ Tan? α = seconds? α; 1+cot? α=csc? α。
Half-angle formula of trigonometric function
sin(α/2)= √(( 1-cosα)/2)
cos(α/2)= √(( 1+cosα)/2)
tan(α/2)=√(( 1-cosα)/(( 1+cosα))?
General formula of trigonometric function
sin(α)=[2tαn(α/2)]/[ 1+tαN2(α/2)]
cos(α)=[ 1-tαN2(α/2)]/[ 1+tαN2(α/2)]
tαn(α)=[2tαn(α/2)]/[ 1-tαN2(α/2)]?
Double angle formula of trigonometric function
Sin2A=2SinA*CosA
cos2a=cosa^2-sina^2= 1-2sina^2=2cosa^2- 1
tan2A=(2tanA)/( 1-tanA^2)