=03sinb=sin(2a+b)可得sin(2a+b)-sinb=2sinb由两角正弦差的公式：sin(2a+b)-sinb=2cos[(2a+b+b)/2]sin[(2a+b-b)/2]=2cos(a+b)sina因此：cos(a+b)sina=sinb,即：cos(a+b)=sinb/sina则：sin(2a+b)=sin[a+(a+b)]=sinaco...