삼각함수 공식.

sin(-θ)=-sinθ, cos(-θ)=cosθ, tan(-θ)=-tanθ

sin²θ+cos²θ=1, sec²θ-tan²θ=1, csc²θ-cot²θ=1

sin(π/2-θ)=cosθ, sin(π/2+θ)=cosθ, sin(θ±π/2)=±cosθ

cos(π/2-θ)=sinθ, cos(π/2+θ)=-sinθ, cos(θ±π/2)=Ŧsinθ

sin(π-θ)=sinθ, sin(π+θ)=-sinθ, sin(θ±π)=-sinθ

cos(π-θ)=-cosθ, cos(π+θ)=-cosθ, cos(θ±π)=-cosθ

sin(α±β)=sinαcosβ±cosαsinβ, cos(α±β)=cosαcosβŦsinαsinβ

tan(α+β)=tanα+tanβ/1-tanαtanβ, tan(α-β)=tanα-tanβ/1+tanαtanβ

sin2θ=2sinθcosθ

cos2θ=cos²θ-sin²θ=2cos²θ-1=1-2sin²θ, tan2θ=2tanθ/1-tan²θ

sin²θ/2=1-cosθ/2, cos²θ/2=1+cosθ/2, tan²θ/2=1-cosθ/1+cosθ

sinαcosβ=1/2{sin(α+β)+sin(α-β)}

cosαcosβ=1/2{cos(α+β)+cos(α-β)}

sinαsinβ=-1/2{cos(α+β)-cos(α-β)}

sinα+sinβ=2sin(α+β/2)cos(α-β/2)

sinα-sinβ=2cos(α+β/2)sin(α-β/2)

cosα+cosβ=2cos(α+β/2)cos(α-β/2)

cosα-cosβ=-2sin(α+β/2)sin(α-β/2)