Khi giải phương trình ![img1](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img1.png)
, ta tiến hành theo các bước sau: Bước
: Bình phương hai vế của phương trình
ta được: ![img5](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img5.png)
Bước
: Khai triển và rút gọn
ta được:
hay
. Bước
: Khi
, ta có
. Khi
, ta có
. Vậy tập nghiệm của phương trình là:
. Cách giải trên đúng hay sai? Nếu sai thì sai ở bước nào?
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img1.png)
![img2](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img2.png)
![img3](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img3.png)
![img4](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img4.png)
![img5](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img5.png)
![img6](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img6.png)
![img7](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img7.png)
![img8](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img8.png)
![img9](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img9.png)
![img10](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img10.png)
![img11](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img11.png)
![img12](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img12.png)
![img13](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img13.png)
![img14](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img14.png)
![img15](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img15.png)
![img16](https://cungthi.online/upload/questionbank3/eduquestion/20184117572112318604/obj20184117572112318604241089_images/obj20184117572112318604241089_img16.png)
A.
Đúng.
B.
Sai ở bước.
C.
Sai ở bước 2.
D.
Sai ở bước .
Đáp án và lời giải
Đáp án:D
Lời giải:
Phân tích: Vì phương trình là phương trình hệ quả nên ta cần thay nghiệm
;
vào phương trình
để thử lại.
Đáp án đúng là D