题目

Every country has its heroes. The heroes are the people the nation and especially the young people admire. If you get a list of the heroes of a nation, it will tell you the potential of that nation. If today in America, you ask the high school students to list their heroes, their choice would probably fall into three groups. The first group of heroes would be the rock stars —the people connected with rock music. There is no doubt that such people do have talent but one wonders if one should regard rock stars as a model. The rock stars too often are involved with drugs and their personal life写出下列分式的最简公分母x+1x，x2x+6，x-1x2-9：______．