並前往http://www.nowforyou.com/math/%E5%82%99%E8%AA%B2/2-1-2%E4%BA%8C%E5%85%83%E4%B8%80%E6%AC%A1%E8%81%AF%E7%AB%8B%E6%96%B9%E7%A8%8B%E5%BC%8F.pdf
