Question

什么是积化和差公式

Answer 1

sinαsinβ = -[cos(α+β)-cos(α-β)]/2 (注意公式前的负号)

cosαcosβ = [cos(α+β)+cos(α-β)]/2

sinαcosβ = [sin(α+β)+sin(α-β)]/2

cosαsinβ = [sin(α+β)-sin(α-β)]/2