sin(A+B) = sinAcosB+cosAsinB

sin(A-B) = sinAcosB-cosAsinB

cos(A-B) = cosAcosB+sinAsinB

tan(A+B) = (tanA+tanB)/(1-tanAtanB)

cot(A+B) = (cotAcotB-1)/(cotB+cotA)

cot(A-B) = (cotAcotB+1)/(cotB-cotA)

倍角公式