1.证明:CD垂直AB,E为AC中点,则DE=AC/2=AE,∠A=∠ADE=∠FDB;又∠A=∠DCG(均为∠ECD的余角).故∠FDB=∠DCB.又∠F=∠F,则⊿FDB∽⊿FCD,FD/FC=FB/FD,FD²=FBxFC.
