Cos2A=CosA^2-SinA^2=1-2SinA^2=2CosA^2-1
(注:SinA^2 是sinA的平方 sin2(A) )
sin3α=4sinα·sin(π/3+α)sin(π/3-α)
cos3α=4cosα·cos(π/3+α)cos(π/3-α)
tan3a = tan a · tan(π/3+a)· tan(π/3-a)
Asinα+Bcosα=(A^2+B^2)^(1/2)sin(α+t),其中
Asinα+Bcosα=(A^2+B^2)^(1/2)cos(α-t),tant=A/B
sin^2(α)=(1-cos(2α))/2=versin(2α)/2
cos^2(α)=(1+cos(2α))/2=covers(2α)/2
tan^2(α)=(1-cos(2α))/(1+cos(2α))