1)证明:AB∥CD,则:∠BDC=∠ABD;
又∠EDB=∠BDC,故∠EDB=∠ABD,得DF=BF.
2)解:设AF=X,则BF=DF=5-X.
AF^2+AD^2=DF^2,即:X^2+9=(5-X)^2,X=1.6
即AF=1.6cm.