A=60°
2c/b-1=(2c-b)/b=tanA/tanB=sinAcosB/cosAsinB
2c/b=(sinAcosB+cosAsinB)/cosAsinB=sin(A+B)/cosAsinB=sinC/cosAsinB=c/bcosA
cosA=1/2,A=60°
A=60°
2c/b-1=(2c-b)/b=tanA/tanB=sinAcosB/cosAsinB
2c/b=(sinAcosB+cosAsinB)/cosAsinB=sin(A+B)/cosAsinB=sinC/cosAsinB=c/bcosA
cosA=1/2,A=60°