sin2a+sin2b=2sin(a+b)cos(a-b)sin2a-sin2b=2cos(a+b)sin(a-b)(sin2a+sin2b)/(sin2a-sin2b)=[2sin(a+b)cos(a-b)]/[2cos(a+b)sin(a-b)]=tan(a+b)/tan(a-b)=-2sin2a+sin2b=-2sin2a+2sin2b3sin2a=sin2bsin2a/sin2b=1/3