解答:解:①根据题意作图得:②∵点D是BC中点,CD=6cm,∴BC=2CD=12cm.∵AB+AB=BC,AC= 1 2 AB,∴ 1 2 AB+AB=12cm,∴AB=8cm,AC=4cm,∴AD=CD-AC=6-4=2cm.
①根据题意作图得:②∵点D是BC中点,CD=6cm,∴BC=2CD=12cm.∵AB+AB=BC,AC=12AB,∴12AB+AB=12cm,∴AB=8cm,AC=4cm,∴AD=CD-AC=6-4=2cm.