OH=OA+AH于是OA+AH=OA+OB+OCAH=OB+OCAH(BC)=AH(OC-OB)=(OB+OC)(OC-OB)=OB²-OC²=R²-R²=0于是AH⊥BC.同理可证BH⊥AC,CH⊥AB,于是H是垂心（2）重心G满足GA+GB+GC=0GA=GO+OA,GB=GO+OB,GC=GO+OC于是3...