a>b>c
则B=60
C=120-A
a/sinA=b/sinB=c/sinC
所以a/c=sinA/sinC
=sin(120-C)/sinC
=(sin120cosC-cos120sinC)/sinC
=3/2*cotC-(-1/2)
0所以cotC>=√3/3
所以m>=3/2*√3/3+1/2=(√3+1)/2