這個函數的傅立葉展開式為

                     

證明 :

                     

                     

                     

                                                             

                          當  

                          當  

                          當 

                          當 

                                             

                                                    

 

      n=1時

傅立葉級數展開式動畫

      n=2時

傅立葉級數展開式動畫

 

      n=3時

傅立葉級數展開式動畫

 

應用:

              令