更新1:
In fact we can use the Squeezing principle (Sandwich theorem) to prove it as follows: 圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Nov08/Crazylim1.jpg aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
