Hệ bất phương trình
có nghiệm khi
A.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037595610_images/obj2018242160364338037595610_img1.png)
B.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037642133_images/obj2018242160364338037642133_img1.png)
C.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037369719_images/obj2018242160364338037369719_img1.png)
D.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037880620_images/obj2018242160364338037880620_img1.png)
Đáp án và lời giải
Đáp án:B
Lời giải:Phân tích:
Ta có ![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img1.png)
.
![img3](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img3.png)
.
Do đó hệ có nghiệm khi
.
Vậy đáp án đúng là B.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img1.png)
![img2](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img2.png)
![img3](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img3.png)
![img4](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img4.png)
![img5](https://cungthi.online/upload/questionbank3/eduquestion/2018242160364338037/obj2018242160364338037307734_images/obj2018242160364338037307734_img5.png)