解：作高AE。∵AB=AC∴BE=CE=1/2BC∵AD⊥AC∴∠CAD=∠CEA=90°∵∠A=∠A∴△CAD≌△CEA∴AC/CD=EC/CA设CE=x,那么CD=2x-BD=2x-1∴（2x-1)*x=6^22x^2-x-12=0x=2(-3/2舍去）∴CD=2x=4cm
上面那个，你6*6变成6*2
