（3）、記 ,求數(shù)列的前項和，并求                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

   （2）、設(shè)，求及的通項；

   （1）、證明數(shù)列是等比數(shù)列；

22、已知,點在函數(shù)的圖像上，其中。

（2）、設(shè)在上是單調(diào)函數(shù)，求的取值范圍。

（1）、當為何值時取得最小值？證明你的結(jié)論；

21、已知函數(shù)