It is known that in quadrilateral ACBD, angle ACB+ angle ADB= 180 degrees, even AB, CD?

1。 When angle ABC= angle BAC=60 degrees, it is proved that DC bisects angle ADB.

2。 Under the condition of 1, let the intersection point A be AH perpendicular to CD and the vertical foot be H, extend the intersection point of AH and BC to E, connect BH, and extend the intersection point of AC to F. If AF=CE and AD=4, find the length of CD.

Note: This is called 20 10 math final exam for grade three.