3.2 sum, difference, and cofunction identities
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Sum and difference identities
Cos(α−β)=cosαcosβ + sinαsinβ Cos(α+β)=cosαcosβ − sinαsinβ Sin(α+β)=sinαcosβ + cosαsinβ Sin(α-β)=sinαcosβ - cosαsinβ Tan(α+β)= ((tanα + tanβ)/(1 − tanαtanβ)) Tan(α−β)= ((tanα − tanβ)/(1 + tanαtanβ))
Cofunctions identities
Sin(90⁰ − θ) = cos θ Cos(90⁰ − θ) = sin θ Tan(90⁰ − θ) = cot θ Csc(90⁰ − θ) = sec θ Sec(90⁰ − θ) = csc θ Cot(90⁰ − θ) = tan θ
reduction formula
Sin(θ + kπ) Sin(θ + 2kπ) Cos[θ + (2k + 1)π]
