7.如图,在三棱锥D−ABCD-ABCD−ABC中,AB=AD=BD=32AB=AD=BD=3\sqrt{2}AB=AD=BD=32,AC=7AC=7AC=7,BC=CD=5BC=CD=5BC=CD=5.(1)证明:平面ACD⊥ACD\botACD⊥平面ABCABCABC;(2)在线段CDCDCD上是否存在一点EEE,使得二面角E−AB−CE-AB-CE−AB−C的正切值为28\frac{\sqrt{2}}{8}82?若存在,求出CECD\frac{CE}{CD}CDCE的值,若不存在,请说明理由.