AF=AC/2 AE=AB/2
BF+CE=AB+AC-(AF+AE)=(AB+AC)/2
BC^2=AB^2+AC^2-2AB*AC*cosA
=(AB+AC)^2-3AB*AC=4(BF+CE)^2-3AB*AC
BF+CE=1/2*√(BC^2+3AB*AC) 只有AB*AC=BC^2 时 BF+CE=BC
AF=AC/2 AE=AB/2
BF+CE=AB+AC-(AF+AE)=(AB+AC)/2
BC^2=AB^2+AC^2-2AB*AC*cosA
=(AB+AC)^2-3AB*AC=4(BF+CE)^2-3AB*AC
BF+CE=1/2*√(BC^2+3AB*AC) 只有AB*AC=BC^2 时 BF+CE=BC