查                     ② y=x2-2x+1-5                                                                                                                                                                                                                                                                                                                                                                                                                                                                     有什么疑惑？

                     ③ y=(x-1)2-5                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

               以上变形是否有错，如果有错，从第几步开始出错，错在哪里？应如何改正？