题目

Blue's CluesPeople around the world are familiar with cartoon series for its early childhood development skills. The cartoon series have ever won nine Emmy Awards because of the lovely dog. And Blue's Clues keeps a great source for children of all ages.Santa's Little HelperSanta's Little Helper is a cute, but poorly trained greyhound.（灰狗）The greyhound has been a gatekeeper for the Simpson household for years. Finally he was replaced by well trained Laddie. Even so, Santa's Little Helper has stayed with the Simpsons ever since.Brian GriffinThe Griffin's dog is well known for his intelli阅读下面材料：小明遇到这样一个问题：如图1，△ABC中，∠A=90°，∠B=30°，点D，E分别在AB，BC上，且∠CDE=90°．当BE=2AD时，图1中是否存在与CD相等的线段？若存在，请找出并加以证明，若不存在，说明理由．小明通过探究发现，过点E作AB的垂线EF，垂足为F，能得到一对全等三角形（如图2），从而将解决问题．请回答：（1）小明发现的与CD相等的线段是_____．（2）证明小明发现的结论；参考小明思考问题的方法，解决下面的问题：（3）如图3，△ABC中，AB=AC，∠BAC=90°，点D在BC上，BD=2DC，点E在AD上，且∠BEC=135°，求的值．