sinA+B = sinAcosB+cosAsinB。推导公式如下:
sin(a+b)=cos(π/2-(a+b))=cos((π/2-a)-b)=cos(π/2-a)cosb+sin(π/2-a)sinb
=sinacosb+cosasinb。
两角和公式
sin(A+B) = sinAcosB+cosAsinB
sin(A-B) = sinAcosB-cosAsinB
cos(A+B) = cosAcosB-sinAsinB
cos(A-B) = cosAcosB+sinAsinB
tan(A+B) = (tanA+tanB)/(1-tanAtanB)
tan(A-B) = (tanA-tanB)/(1+tanAtanB)
cot(A+B) = (cotAcotB-1)/(cotB+cotA)
cot(A-B) = (cotAcotB+1)/(cotB-cotA)