sinA+sinB=2cos(A+B)/2*Sin(A-B)/2 - =2sin(A+B)/2*cos(A-B)/2 cosA+cosB=+2cos(A+B)/2*cos(A-B)/2 - =-2sin(A+B)/2*sin(A-B)/2 tanA+cotA=2/sin2A tanA-cotA=-2cot2A cosA*sinB=1/2[sin(A+B)-sin(A-B)] cosA*cosB=1/2[cos(A+B)+cos(A-B)] sinA*sinB=-1/2[cos(A+B)-cos(A-B)] tanA/2=sinA/(1+cosA)=(1-cosA)/sinA