证明：∵DE⊥AC于E∴Rt△ADE相似于Rt△ABC∴BC/AC=DE/AE（1）∵DF⊥BC于F∴Rt△DBF相似于Rt△ABC∴BC/AC=BF/DF（2）∵CD...第一小问会做TAT求第二问等我弄个图，稍等:∵∠A=∠BCD(均为角B的余角);∠AED=∠CDB=90度.∴⊿AED∽⊿CDB,CD/AE=BC/AD;-----------------------(1)同理相似可证:⊿ADC∽⊿DFB,CD/BF=AD/DF;--------(2)⊿CFD∽⊿ACB,CD/AB=DF/BC. -------------------------(3)∴(1)x(2)x(3),得:(CD/AE)x(CD/BF)x(CD/AB)=(BC/AD)x(AD/DF)x(DF/BC)=1.即:CD³/(AExBFxAB)=1, AExABxCD=CD³.图传不了，这个是过程