问题
选择题
已知二次函数y=ax2+bx+c的部分对应值如下表所示，则不等式ax2+bx+c＞0的解集为（ ）
|
答案
通过从图中可看出：
二次函数y=ax2+bx+c开口向下，且有两个零点：-1，3；
故不等式ax2+bx+c＞0的解集为-1＜x＜3．
故选C．
搜题请搜索小程序“爱下问搜题”
已知二次函数y=ax2+bx+c的部分对应值如下表所示，则不等式ax2+bx+c＞0的解集为（ ）
|
通过从图中可看出：
二次函数y=ax2+bx+c开口向下，且有两个零点：-1，3；
故不等式ax2+bx+c＞0的解集为-1＜x＜3．
故选C．
| 完形填空。 | ||||
| Can you imagine what life would be like if there was no telephone? You could not 1 your friends on the phone and talk to them. lf fire 2 out to your house, you 3 call the fire department. If somebody 4 sick, you could not call a doctor. In our 5 life we need to communicate with 6 .We do this 7 by speaking to other people and listening to what they have to say to us, and when we are 8 to them, we can do this very easily. 9 ,our voices will not travel very far even when we 10 , and it is thanks to the 11 of the telephone that we are 12 able to communicate with each other 13 hold talks when we are far apart. We can hear each other 14 clearly as if we 15 in the same room. The man who made this 16 was Alexander Graham Bell, a Scotsman, born in Edinburgh in 1847. Bell, a teacher of visible speech (可视语言 ), who later moved to Canada, 17 all his time experimenting. 18 enthusiastic(热情的) was he in his research for means for 19 speech by electricity that he left 20 time for his day-to-day work and at one time was almost penniless (身无分文). | ||||
|