Trigonometric function formulas include product sum and difference formula, sum and difference product formula, triple angle formula, sine double angle formula, cosine double angle formula, cosine theorem, etc.

1 Product sum and difference formula. sinα·cosβ=(1/2)*[sin(α+β)+sin(α-β)]; cosα·sinβ=(1/2)*[sin(α+β)-sin(α-β) ];cosα·cosβ=(1/2)*[cos(α+β)+cos(α-β)]; sinα·sinβ=-(1/2)*[cos(α+β)-cos(α -β)]

2. Sum-difference product formula. 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]

3 Triple angle formula.

sin3α=3sinα-4sin^3α: cos3α=4cos^3α-3cosα

4 The trigonometric function relationship between the sum and difference of two angles sin(α+β)=sinαcosβ+cosαsinβ;sin(α-β)= sinαcosβ-cosαsinβ;cos(α+β)=cosαcosβ-sinαsinβ;cos(α-β)=cosαcosβ+sinαsinβ;tan(α+β)=(tanα+tanβ)/(1-tanα·tanβ);tan(α -β)=(tanα-tanβ)/(1+tanα·tanβ)