[DS12.C1.2.D16.c] Gọi
là tập hợp tất cả các giá trị nguyên của tham số
để hàm số
có
điểm cực trị. Tìm số phần tử của
.
A.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668408251_images/obj20200509928840646668408251_img1.png)
B.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668643802_images/obj20200509928840646668643802_img1.png)
C.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668163963_images/obj20200509928840646668163963_img1.png)
D.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668718453_images/obj20200509928840646668718453_img1.png)
Đáp án và lời giải
Đáp án:C
Lời giải:
Theo mình: Hàm số
có
điểm cực trị khi và chỉ khi phương trình
có
nghiệm phân biệt.
Xét hàm số
, ta có
.
![img7](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img7.png)
.
Suy ra hàm số đã cho có
điểm cực trị khi và chỉ khi
.
Vậy
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img1.png)
![img2](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img2.png)
![img3](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img3.png)
![img4](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img4.png)
![img5](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img5.png)
![img6](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img6.png)
![img7](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img7.png)
![img8](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img8.png)
![img9](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img9.png)
![img10](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img10.png)
![img11](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img11.png)
![img12](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img12.png)
![img13](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20200509928840646668/obj20200509928840646668399585_images/obj20200509928840646668399585_img13.png)