This " method of construction " ( realized through the method of completing square ) is far conciser than my classification method and i feel pleasantly surprised at the beauty of concision from the standard solution 这个"构造法" （通过配方法实现） ，比我采用的分类处理法不知要简洁多少倍，标准解答所散发的简洁美令我感到惊喜。
