tanA/tanB= sinAcosB/sinBcosA c=2RsinC b=2RsinB所以 2 x 2RsinC - 2RsinB / 2RsinB = 2sinC-sinB/sinB所以sinAcosB/sinBcosA = 2sinC-sinB/sinB化简得sinAcosB+cosAsinB=2sinCcosA 又 sinC=sin(180°- (A+B))=sin(...