∵AC⊥BC ,CD⊥AB
∴∠BCD=∠A ,
∵Rt△ACD∽Rt△ABC
∴AC^2=AD*AB =m(m+n)
又∵Rt△BCD∽Rt△ABC
∴CD^2=BD*AB =n(m+n)
∴AC^2/BC^2 =m/n