2.
如图\(①\)所示,平面五边形\(ABCDE\)中,\(AB/\!/CD\),\(∠BAD=90^{\circ}\),\(AB=2\),\(CD=1\),\(\triangle ADE\)是边长为\(2\)的正三角形\(.\)现将\(\triangle ADE\)沿\(AD\)折起,得到四棱锥\(E - ABCD(\)如图\(②)\),且\(DE⊥AB\).
![](https://www.ebk.net.cn/tikuimages/2/2018/700/shoutiniao89/23e4de6e033e0e83873f616502756dda.png)
\((1)\)求证:平面\(ADE⊥\)平面\(ABCD\).
\((2)\)求平面\(BCE\)和平面\(ADE\)所成锐二面角的大小.
\((3)\)在棱\(AE\)上是否存在点\(F\),使得\(DF/\!/\)平面\(BCE?\)若存在,求\(\dfrac{{EF}}{{EA}}\)的值\(;\)若不存在,请说明理由.