∵CD⊥AB
∴∠ADC＝90
∴CD＝√（AC²-AD²）＝√（36-16）＝2√5
∵∠C＝90,∠BAC＝∠CAD
∴△ABC∽△ACD
∴AB/AC＝AC/AD,BC/AC＝CD/AD
∴AB/6＝6/4,BC/6＝2√5/4
∴AB＝9,BC＝3√5