3(cosB^2-sinB^2)+2sinBcosB+sinB^2+cosB^2=04cosB^2+2sinBcosB-2sinB^2=0(4cosB-2sinB)(cosB+sinB)=0B为内角,A=π/3,所以cosB+sinB>0所以4cosB-2sinB=0tanB=2B=2π/3-C(tan2π/3-tanC)/(1+tan2π/3tanC)=2tan2...