题目

  BEIJING, Oct. 1(Xinhua)—Police across China have got ready to deal with huge traffic flows along expressways during the eight-day national holiday, said the Ministry of Public Security here Monday. Traffic along main expressways increased by more than 40 percent on Sunday, the first day of the holiday period, said a statement on the ministry website. Police have opened 743 service stations along expressways and set up to 14, 000 temporary service booths to help control traffic, the statement said. In addition, more than 16, 000 ambulances have been put on standby for emergencie已知二次函数y=x2+bx+c的图象与x轴只有一个公共点A．（1）若这个公共点为（2，0），求二次函数的表达式；（2）若二次函数的图象与y轴的交点为B，坐标原点为O，且△OAB是等腰三角形，求该二次函数的表达式，并说明它是如何由（1）中的二次函数的图象平移得到的．