tan(A+B)=tan(2C)=-tanC=2tanC/(1-(tanC)^2)
tanC=根号3 tan(A+B)=(tanA+tanB)/(1-tanAtanB)=-根号3
tanA+tanB=2根号3 tanAtanB=3 tanA=tanB=根号3
A=B=C=60°
tan(A+B)=tan(2C)=-tanC=2tanC/(1-(tanC)^2)
tanC=根号3 tan(A+B)=(tanA+tanB)/(1-tanAtanB)=-根号3
tanA+tanB=2根号3 tanAtanB=3 tanA=tanB=根号3
A=B=C=60°