在本論文中,我們完整的證明了Dirichlet’s theorem。另外,我們針對在Quadratic fields中的L-series作研究,寫成許多不同的形式。利用L-series在s=1時的不同形式可推導出class number的一些公式。由class number最後推導出的公式可看出quadratic residues和quadratic nonresidues的個數在區間 (0,p/2) 的分布情形。最後,我們給了一些在quadratic fields中,L-series在s=1時,用不同的character代入所得到的特殊值。
In this thesis, we first review some well-known results about the Dirichlet characters and L-series. Then we give an elaborate proof of Dirichlet's theorem. Besides, we are interesting in the formulas of L-series associated to the quadratic fields. Then we compute class numbers of quadratic fields with L-series at $s=1$ and the Gaussian sum. In the end, examples of L-series at $s=1$ are given.