问题
填空题
已知集合M={x|ax2+2x+1=0}只含有一个元素，则a=______．
答案
∵集合M={x|ax2+2x+1=0}只含有一个元素，当a≠0时，有判别式△=4-4a=0，解得a=1．
当a=0时，集合M={-
}只含有一个元素，满足条件．1 2
综上可得，a=0或a=1，
故答案为 0或1．
搜题请搜索小程序“爱下问搜题”
已知集合M={x|ax2+2x+1=0}只含有一个元素，则a=______．
∵集合M={x|ax2+2x+1=0}只含有一个元素，当a≠0时，有判别式△=4-4a=0，解得a=1．
当a=0时，集合M={-
}只含有一个元素，满足条件．1 2
综上可得，a=0或a=1，
故答案为 0或1．
| 完形填空。 | |||
| Agatha Christic would never forget the night when she met a robber (抢劫者)many years ago. That evening, she went to a birthday party which 1 until two o'clock in the morning. Agatha walked in the 2 street alone. Suddenly from the back of a dark 3 a tall man with a sharp knife in his right hand ran out at her. "Good 4 , lady," the man said in a low voice. "I don't think you wish to 5 here!" "What do you want?" "Your earrings. Take them off!" Agatha suddenly had a 6 idea, She tried to cover her necklace with the collar (衣领) of her overcoat while she used 7 hand to take off both of her earrings and then quickly 8 them on the ground. "Take them and let me go," she said. The robber thought that the girl didn't like the earrings at all, only wanted to 9 the necklace. It would cost 10 , so he said, "Give me your necklace." "Oh, sir. It doesn't 11 much. Please let me wear it. " "I'm not that 12 . Quick!" With shaking 13 Agatha took off her necklace. As soon as the robber left, she picked up her earrings and ran as 14 as she could to one of her friends. The earrings cost 480 pounds and the necklace the robber had taken away cost 15 six pounds. | |||
| ( )1. A. ended ( )2. A. busy ( )3. A. part ( )4. A. morning ( )5. A. die ( )6. A. funny ( )7. A. other ( )8. A. handed ( )9. A. own ( )10. A. cheap ( )11. A. weigh ( )12. A. afraid ( )13. A. hands ( )14. A. much ( )15. A. really | B. stayed B. quiet B. block B. afternoon B. escape B. safe B. others B. threw B. keep B. expensive B. take B. angry B. feet B. early B. already | C. stopped C. noisy C. building C. evening C. fight C. brave C. the other C. passed C. have C. more C. spend C. silly C. head C. carefully C. only | D. lasted D. wide D. street D. night D. stay D. bright D. another D. put D. protect D. less D. cost D. bad D. body D. fast D. hardly |
