AB=√(AC^2+BC^2)=10;BC'=BC=6,則AC'=4.
∠BC'D=∠C=90°,則∠AC'D=∠C=90°;
又∠A=∠A,故⊿AC'D∽⊿ACB,AC'/AC=AD/AB.
即:4/8=AD/10,AD=5,CD=AC-AD=3,BD=√(CD^2+BC^2)=3√5.