所以，△ABC面积是                                           14分

由得，,                                               12分

（Ⅱ）由可得，，                               9分

又，∴  。                                                7分

，                                 5分

15．解：（Ⅰ）由得，，                      3分

13．                              14．

9．1                                  10．                        11．                  12．

5．1                                   6．                     7.               8．

1．    2．                      3．                        4．