$解:過點?D?作?DF⊥BC,?垂足為點?F?$
$∵?AB⊥BC,?點?B?在?\odot O?上$
$∴?CB?是?\odot O?的切線,?B?為切點$
$∵?AD//BC,?點?A?也在?\odot O?上$
$∴?AD?也是?\odot O?的切線,?A?為切點$
$∵?CD?也是?\odot O?的切線,且點?E?為切點$
$∴?AD=DE=a,??CE=BC=b?$
$∴?CD=a+b?$
$∵?DF⊥BC?$
$∴?CF=b-a,??DF=AB=2?$
$在?Rt△DFC?中,?CD^2=DF^2+FC^2?$
$?(a+b)^2=(b-a)^2+2^2?$
$∴?ab=1?$