（Ⅰ）求证：AE⊥平面BCE；

（Ⅱ）求二面角B﹣AC﹣E的余弦值；

（Ⅲ）求点D到平面ACE的距离．

                                                                                                            兰溪棹歌^①
                                                                                                               戴叔伦
                                                                                     凉月如眉挂柳湾，越中山色镜中看。
                                                                                     兰溪三日桃花雨，半夜鲤鱼来上滩。
                                                              【注释】①兰溪，在今浙江兰西县西南。棹（zhào）歌：船歌。