因为a,c,b成等比
所以(sinC)^2=sinAsinB
sinCsin(A+B)=sinAsinB
sinC(sinAcosB+sinBcosA)=sinAsinB
sinC(tanA+tanB)=tanAtanB
tanC=2sinC=2cosCtanC
cosC=1/2
因为 0
因为a,c,b成等比
所以(sinC)^2=sinAsinB
sinCsin(A+B)=sinAsinB
sinC(sinAcosB+sinBcosA)=sinAsinB
sinC(tanA+tanB)=tanAtanB
tanC=2sinC=2cosCtanC
cosC=1/2
因为 0