根据同一三角形的底与高成反比设Ha=4s,Hb=3s,Hc=2s所以(Ha+Hb+Hc)(1/Ha+1/Hb+1/Hc)=(4s+3s+2s)(1/4s+1/3s+1/2s)=9s*(13/12)/s=39/4