根据正弦定理,有
tanB/tanC=(2sinA-sinC)/sinC
化简有,
sinB*cosC/cosB=2sinA-sinC
sinB*cosC=2sinA*cosB-cosB*sinC
sinB*cosC+cosB*sinC=2sinA*cosB
sin(B+C)=2sinA*cosB
sinA=2sinA*cosB
因此,cosB=1/2.
因此B=60度.tanB/tanC=(2sinA-sinC)/sinC如何化简为sinB*cosC/cosB=2sinA-sinC?