lgtanA+lgtanC=2lgtanB
则lg(tanAtanC)=lg(tanBtanB)
tanAtanC=tanBtanB
设tanA=a/q,tanB=a,tanC=aq,a>0,q>0
则tanC=-tan(A+B)=-(tanA+tanB)/(1-tanAtanB)
aq=-(a/q+a)/(1-aa/q)
得a^2=q+1+1/q>=3
tanB=a>=根号3
60
lgtanA+lgtanC=2lgtanB
则lg(tanAtanC)=lg(tanBtanB)
tanAtanC=tanBtanB
设tanA=a/q,tanB=a,tanC=aq,a>0,q>0
则tanC=-tan(A+B)=-(tanA+tanB)/(1-tanAtanB)
aq=-(a/q+a)/(1-aa/q)
得a^2=q+1+1/q>=3
tanB=a>=根号3
60