题目

已知向量，，.（1）若，，求实数的值；（2）记，若恒成立，求实数的取值范围. 答案：【答案】（1）-2或2.（2）【解析】（1）由可得,进而求解即可；（2）由可得,由可得,若恒成立,则,再分类讨论与的情况,进而求解即可.解:（1）因为,所以,即,因为,所以,故,当时,显然不成立,故,所以,解得或2,所以实数的值为或2（2）,因为,所以,所以,因为恒成立,所以,当时,,显然成立；当时,,所以,解得,所以,综Dear Jack,    I had a very unusual e__________ on Sunday．At around ten o’clock in the morning, I was walking d______ the street when a UFO landed in front of me．You can imagine how s_________ it was! An a________ got out and walked down Center Street． I f________ it to see where it was going, and I was s________ when it went into a souvenir shop． While it was looking at the souvenirs, the shop a_________ called the police．Before the police arrived, the alien left the shop and visited the M_______ of Flight．W_______ the alien was in the museum, I called the TV station．Isn’t that a________!