积化和差公式:sinAcosB=1/2[sin(A+B)+sin(A-B)
]sinBcosA=1/2[sin(A+B)-sin(A-B)
]sinAsinB=1/2[cos(A+B)-cos(A-B)
]和差积化公式:sinA+sinB=2[sin(A+B)/2]*[cos(A-B)/2]sinA-sinB=2[cos(A+B)/2]*[sin(A-B)/2]cosA+cosB=2[cos(A+B)/2]*[cos(A-B)/2]cosA-cosB=-2[sin(A+B)/2]*[sin(A-B)/2]